I am going to go above and beyond and do ALL of them. I'll try to provide explanations but some it's just '....yeah, I like it'.
No particular order. Just categories.
The Very Best That No One Ever Was
ANGERME - Because it made a whole lot of people mad, and the jokes write themselves. Everyone go home, because no name will ever top this.
Good
Buono! - Short, memorable, and it means good, which they always were.
Cat's♥Eye 7 - This name is kind of sexy in an idol sort of way, and I thought their MV and song fit the name.
DEF.DIVA - Maybe not Nacchi, but the other three are definitely the definitive divas of H!P, so this name is cool and makes sense to me.
Ecomoni - Same as Mini Moni and Petit Moni, although it was a bit played out by the time this unit came along.
GREEN FIELDS - Almost sounds like it could be some soft rock Japanese band name. Boring like Harvest, but it got the job done.
Harvest - Boring, but it fit the Satoyama theme, and that's more than a lot of H!P names can say.
Hello Pro Kenshuusei - I guess it's not inspiring, because it's exactly what the program is, but there's literally nothing even remotely bad about it other than the fact that a lot of people forget they're this and not the Eggs anymore. No reason to put it on anything other than the Good list.
High-King - H!P Wiki informs me that Tsunku said this group should have been called High Queen but it didn't have enough punch and also "the members were chosen for their ability to dance and belt out dancable R&B numbers". This is laughable as Yuuka never belted a note in her life. This unit is really overrated in my opinion, but their name is cool.
Kira☆Pika - Sounds like an anime unit, and is an anime unit.
MilkyWay - Same as
Kira☆Pika.
Mini Moni - A group made up of mostly MM members who were quite mini. Makes sense to me.
Morning Musume - When you look at names from newer debuted groups, you can tell MM is an old name, but it gives off that old classic 90s idol vibe and I like it. It's an oldie but a goodie.
Morning Musume Tanjou 10nen Kinentai - WhatItSaysOnTheTin/10.
Petitmoni - None of these girls were petite, but unlike Country and Coconuts, at least they were directly related to MM.
S/mileage - It was one of the few explanations for a name that Tsunku ever gave that was cute and made sense. Kana said that they received 10k new name submissions and a lot of them were S/mileage. It was a good one and I'll miss it.
Sheki-dol - I don't know what the Sheki stands for, but I've always liked this name a lot for no reason. Also, Tetteiteki Unmei is awesome.
Shugo Chara Egg! - Like Kenshuusei where it was exactly what it said it was. Shugo Chara was cute, Eggs was a cute name, and the members/outfits/songs were cute as well. Cute/10.
Tanpopo - It's a nice name. That's it.
W - Hardest name ever to google, but the pun was fun.
Sort of Good
Berryz Kobo - Cute when they were 10-12, but it's a name that didn't grow up with them.
℃-ute - Same as Berryz, but to an even greater extent now that they like to pole dance and shake their butts. Also, including the degree is hard.
DIY♡ - It's very cute but since the name actually stands for Dance In Your Heart, which isn't at all obvious, I can't put it on a best. Forever a DIY project, which is an accurate description of the quality of H!P MVs (although DIY's MV was actually kinda ok iirc)
Guardians 4 - When I think Guardians 4,
I think of the kind of music that Stardust's Tenkasu Trio sings.
Melon Kinenbi - I cannot for the life of me remember what Kinenbi means, and neither can the internet, but I'm guessing it's a bit too nonsensical for me to put them on the Good list.
Otome Gumi / Sakura Gumi - ....yeah, they're alright.
v-u-den - Has a cool meaning, but the romanisation just looks like nonsense.
Not Good
4KIDS - There were 4 of them and they were kids who came from H!P Kids!!!!! I'm just not feeling it.
Aa! - Is this supposed to be the noise you make after your first kiss? It's just a bit odd.
Coconuts Musume - Same as Country Musume, except no one pitied them enough to give them a MM member to help them out.
Country Musume - Lame ploy used to cash off of MM's success that never worked without adding actual MM members.
Ex-ceed! - I won't post the rationale behind the name here, but you can find it on the H!P wiki to see how silly it is.
GAM - I know a lot of people will probably disagree, but I always thought this name was dumb.
Kobushi Factory - Probably not what most people will consider oh my god terrible, but like I said in their thread, I think the group deserves to have their own identity that isn't connected to an old group. H!P always looks to the past and never to the future blah blah ect.
Lilpri - I think it's short for Little Princess. Rolls off the tongue odd and brings up memories of their hilariously bad wigs.
Mobekimasu - Ugly to say and doesn't work for a program that doesn't have the same constant lineup. Also their only song sucked.
Morimusu - See the Zenrokyu ect. Musume name below.
Muten Musume - By the time this group came about, putting Musume at the end of something didn't make people care about it. Should have tried harder. Also, unit names when it includes the entire original group are pointless.
Nochiura Natsumi - You can't tell at first but it is a member name inspired group name, so duh, I don't like it.
ODATOMO - Makes me think of tomatoes.
Ongaku Gatas /
Gatas Brilhantes H.P. - Gatas means to crawl, which you probably shouldn't do onstage, because a lot of feet have been on it.
Reborn Eleven - Yawn.
ROMANS - The Roams wore nighties and rapped. Not great, but I don't think it's bad either. I threw it down here because you're supposed to pronounce it Romance, so why didn't they just CALL THE UNIT ROMANCE FROM THE START?
Sato no Akari - I don't like group names that play off member names, and their lineup sucked to boot.
SI☆NA - Like Sato no Akari, I don't like names that play off member names. Also, these poor flops that never stood a chance. : ( It's amazing how long UFP wasted their time.
Taiyou to Ciscomoon / T&C Bomber - Like MM, they give me a definite 90s vibe, but what does Ciscomoon even mean? I know a dog named Cisco.
Triplet - Would have been cute if they were members that were known for looking alike, but they don't.
Zenryoku Yasai Musume + - I didn't know they came up with a name for the Kagome campaign. Either way, the Musume name trend is like beating a dead horse in 2014 and why not just do this campaign as Morning Musume '14?
ZYX - Proof that Tsunku or whoever came up with this name will be golden if he/they gets pulled over in the US as long as he passes the breathalyzer test. Not pronounced individually, though, so it sounds dumb.
Why?
Athena & Robikerottsu - If there's actually a character named Athena in this anime, I guess you could move this into Not Good. Still looks dumb, though.
Country Girls - Makes me think of a bunch of bumpkins and rednecks, many of whom I'm either related to or went to school with. And like the Factory Group, I hate that so much in H!P has to be a revival and an attempt to cash off of nostalgia.
Gomattou - I know that this is like the one unit in H!P that almost no one likes it when they get slammed, but I really hate this name. I also hate their song, sorry.
Ice Creamusume - This is stupid.
Juice=Juice - If Juice were a number, that statement would be true, but it's still dumb. Also doesn't fit the vibe I get from the group at all.
Jurin - What did this name even mean?
Metro Rabbits H.P. - What does this have to do with kickball?
Morning Musume '# - Although not awful by looks, it serves no useful purpose other than cluttering up any site that sells MM merchandise. Forever dumb.
Peaberry - I like to eat peas, but they are not berries. And now that I love Dawa, I'm bitter she got paired with a voice I can't stand on top of having a boring song.
POCKY GIRLS - It may have been for a Pocky CM, but it's still dumb to me. They also had the inferior song on the 5th album to make matters worse. The Mousse song >>> This song.
Tomoiki Ki wo Uetai - I don't think they ever planted a single tree.
Ujicha♥Taishi Maccha's - A name about green tea, for a unit that only talked and sang about green tea. I think this speaks for itself.
Venus Mousse - Their song was better, but their name is just as stupid as Pocky Girls.
Honorable Mention Towards Two Groups That Made Me Go "Who the fuck is this?"
Ujicha♥Taishi Maccha's
Zenryoku Yasai Musume
But maybe Thea had it right, because in H!P if you aren't really good, you're probably awful. So 0/10 to anyone who isn't called Angerme, the best group name that ever was.
It was really sad how I immediately recognized most of these names, as well as what their songs were and who was in the group. I need a life.