HTC --- I've been very happy with them so far all the way back to my WinMo and early Android days. I wanted a Desire HD, but got a Desire Z instead. I like what I see with the Desire S, Incredible S aka Droid Incredible 2, and the HTC Senstation is heading to the top of my list.
Samsung --- Of all my Androids I hated the most was my Samsung Galaxy S and at one time, after throwing the phone at the wall --- where it survived without a scratch --- I swore I won't buy a Samsung again. That was before I ended up buying a Galaxy Tab and the Nexus S. Both of whom were really good. The Galaxy SIi is now top of my list.
Motorola --- My Android experience seems incomplete without having to try a Moto phone at least once. Nearly got an Atrix, the latest of a long list of "nearlys" that include the Droid, Droid 2 and Droid X. but eyeing a Droid X2 now as a possible replacement to my Droid Incredible.
Sony Ericsson --- Really like the new designs and the Play got my curiosity.
LG --- I'm liking what I see with their latest phones. LG traditionally makes solid well built phones but albeit with a certain blandness. The Avis to Samsung's Hertz. If they make the next Nexus, that would be a sure buy for me.