Emgo316 is probably my number 1. He's hilarious, I LOVE Mascot, and I find his reviews to be extremely informative, especially when it comes to a figure's transformation.
Second would be TJOmega (aka "The Plastic Addict"). His reviews are also amusing and informative.
I like thecollector75 a lot. He reviews a wide variety of figures, including current, G1/Beast Wars and even 3rd party and KO's.
There's a fairly recent reviewer, Mitch Santona, that I've been watching quite a bit lately. He does some great reviews, great quality video and he's generally on top of the latest releases.
I like WolfKang1's reviews. He doesn't do them too often, but when he does, if a figure is SHIZZLESNIT, he definitely lets you know about it.
I watch quite a few of baltmatrix's reviews. He does a lot of figures from older lines, including Beast Wars and stuff that's more obscure, like Animorphs and such so it's great for learning about figures I wasn't aware of.
I used to watch MindZombie and ExillionXLR, but neither have done anything recently (kinda sucks because MindZombie did a ton of Beast Wars reviews, my favorite line of all time
). Exillion was hilarious.
Mattersmasher was another Beast Wars fan/reviewer, but he hasn't done anything recently either.
I like Thew, his short reviews are hilarious.
I occasionally watch Vange1us. I had quit watching him for a while, but recently he's been reviewing more TF's (especially Arms Micron figures, doing what he refers to as 'V-builds' where he builds the Microns and applies the stickers on camera) so I've been watching him again.
I used to watch both Peaugh and Optibotimus, but I haven't watched them in many months. I kinda got tired of both of them for some reason (I detest Peaugh's intro music for one thing