Sten was so hard to get along with and his banter wasn't always that fun or insightful. I also never had any use for a two hander. Alistair, Morrigan, Doggy/Zev, Oghren/Shale, Leliana (as long as I don't have to listen to her bond with Wynne and talk about how sweet the other is) and then Sten. Alistair pulls so much threat he's the greatest tank, and he's the other warden so it feels like he should be in the party. Morrigan is deadly and makes a great healer.
I don't really have just one favorite. I tend to take Alistair, Zevran, and Morrigan (if I'm not a mage) or Barkspawn/Apawstate or Shale (if I am a mage). I like the other characters.....just not as much as the ones I think of as my 'core' party.
Same thing for DA:2 (Anders, Fenris and Varric) and DA:I (Bull, Dorian and Varric)
I base it on who is most useful, who 'fills out' the party, and who has the best banter. XD
I realize that all the love interests that I like are in my party in every game, except for Cullen, (Damn you BioWare for not letting him join in on the fun killing sprees, and also for not letting us date Varric!) but they are my LI's because they are my favorite characters! I can't stand stuck up Solas, Sera is a bit too annoying, Josie is too high maintenance, Lili appeals to me like a sister, Blackwall's beard is just too much....BEARD...for me. LOL Cass seems like she might be a good LI though for my next play through...if i can avoid Cullen's cuteness, Dorian's sexy confidence or Bull's duality of assertiveness and hidden need to be loved/snuggled!