Multiplayer: I like all the Quarian kits, especially the QME, QFI and Quarksman. I'd say they're my most-used alien race besides Drell and Asari. Sabotage isn't a very good power these days, but TacScan, Incinerate and both Sticky and Arc Grenades are all great powers, and TC and Marksman are of course super strong.
Singleplayer: For the most part, I side with the Quarians, but constantly question the invention of the Geth and the ethics of experimenting on them. I always compromise if possible, since most compromises ****** off the Admiralty, and trolling them is always enjoyable. The Quarian Admiralty reminds me of Bhelen in DA:O; I find a lot of what they do to be repugnant, but siding with the other party instead will mean much, much worse (since in this case, a whole species is exterminated as opposed to a line of computers). I compromise for both the Quarians and Geth, but the Geth being wiped by Destroy is a small price to pay for the elimination of the Reapers--they were tainted with the Reaper Code. Tali is one of my favorite characters and I think she got better character development than anyone else, even Mordin and Wrex. I also think that she is by far the most interesting and best romance for a paragon male Shepard. I've played other alignments and romanced other characters, but I haven't done a 1-2-3 import playthrough with any other setup, because anything else feels underwhelming. Ashley's effectively only in one-and-a-half games if she survives Virmire, I detest Liara's writing, and everybody else isn't in the first game and/or plays an extra after the second game. Oh and I really liked Kal'Reegar, the only Quarian in the whole Migrant Fleet who wasn't bound in politics, and a champion for all his people. Kind of BS that he dies in ME3.