I'd root for Brooklyn easily.
Multiple factors:
Them coming to NY and winning a title almost right away over the Knicks AND having Pierce be a big part of it. I am a big Knick hater so this would be really awesome and funny to see happen. I really hope they match up and the Nets can beat them in the playoffs.
KG and Pierce. It's pretty amazing looking back there was only one title for the big three (homerism, sure, but you would have figured at least 2.) They both deserve to win more than one title and I don't think that takes anything away from them being Celtics. In particular KG, a guy who is pretty much the ultimate teammate, deserves to win more than one title in his career. But either way, love both players so much and just want to see them succeed.
Doc. Well I don't hate him or anything, but I do think less of him because he just bailed on rebuilding. If that isn't what he wanted to do, I get that, but then just respect him less than I used to. I love what he did with the Celtics and think he's a good coach, but I am not rooting for Doc Rivers to win anything now. He's just another coach, and I don't particularly like the Clippers, between Sterling and Blake Griffin.