Wings of Honor. Because it's the only one I have!
The G2 set looked impressive. I did snag G2 Breakdown and I do like him, especially thanks to his connection to past Botcons. Of the Wings set I really like Scourge. Still! If I had to do it all over again, I'd probably still get him. The color choices on him are fantastic.
The Pre-Beast Wars set also seemed great. That's probably their best. Not only for the toys themselves, but the concept really hit it out of the park.
Out of all the figures I've seen online that I didn't buy yet, I'd have to say I still want Deathsaurus. If I ever find him at a reasonable price (not likely).