I can't place what appeals to me most but I think I've always loved futuristic designs ala the War Within and Cybertron series. I'm still waiting on my WW Prowl and Grimlock which I expect I'll love just b/c of the futuristic feel of both alt modes not to mention the characters. Others that come to mind are WW Prime, G1 Cyclonus, the G1 Headmaster jets, the G1 Targetmasters, the Technobots, TFA Cybertron Prime, much of Cybertron and Energon, and, to a lesser extent, Titanium WW Megatron.

Armada's alt modes didn't do much for me. They still felt luck they were stuck between RiD and Energon at that point.

Realism doesn't worry me too much about TFs. As a kid, transforming robots was enough of a stretch for me to give realism a kick right up the rear. I mean, it's nice but hardly necessary.

Oh and base-formers are definitely a favourite of mine too. Small or big, it doesn't matter as long as there's attention to detail. One of the reasons I like Micromasters so much b/c I otherwise I wouldn't even bother collecting them.

The other thing I might add is alt modes of mass destruction. Not necessarily tanks but vehicles that are armed to the max appeal to me too. Sometimes that means a whole lot of guns that pop off and lots of accessories but that doesn't bother me as long as he says "You are toast". TFA Ultra Magnus, G1 Metroplex and Fort Max, Classics Skyfire, Energon Galvatron all come to mind immediately.

This thread was a great idea.