Yeah, I'm going to have to go with the Robot Masters. Although I like the mavericks somewhat in that, at least in X1-X3, their weapons tend to be more useful than Robot Master weapons. In my opinion, at least.
Let's see...
Storm Eagle: Covered a good area, caused loads of damage.
Boomerang Kuwanker (lol name pun!): Basically a Rolling Cutter.
Sting Chameleon: Normal shot had a good spread, charged made it easy to survive.
Flame Mammoth: Sucked for me.
Chill Penguin: Good spread on impact + usefull charge shot.
Launch Octopus: Meh! Didn't like it at all.
Armored Armadillo(?): Trolling ball is good, but shield is meh.
Spark Mandrill: Interesting weapon, but could be much better.
Whell Gator: Good damage, spreadshot with charged.
Magna Centipede: Remote Mine anyone? Charge rips through enemies.
Crystal Snail: Mostly useless. Only use I ever found was to "create" platforms.
Flame Stag: Fireballs with good damage and an airdash. Great if comboed with your regular air dash.
Wire Sponge: Useless weapon. Good only for getting to wall or getting items.
Overdrive Ostrich: Good weapon, but awkward to use. Charge Shot proves usefull to kill enemies out of reach.
Morph Moth: Bad weapon too. Only use I had for it was to fill tanks and lives in "Secret Spots".
Bubble Crab: Should be Nerf Crab. Also, chrage shot drains your ammo.
Neon Tiger: Good charge and normal. No complaints.
Toxic Searhorse: Salt Water from Megaman V GB. Useless.
Blizzard Buffalo: Nice Shield and missile. It had other uses, I guess? Oh, underwater it became stronger.
Drill Rhino: Hated him and his weapon. Bust proves to help a bit.
That's all I remember as of now