My direct opponents: I fought people in TOP, TSO and FEAR. I was left unimpressed by the FEAR opponent, while I'd say that my TSO and TOP opponents were at the same sort of (decent) level on average, but TOP's fighters tended to be a little more erratic than TSO's - either very good or not very good. Small sample size, of course.
TSO had the best banter.
As I say, you only get a small sample, and although you can get a decent understanding of how proficient your opponents are from a 7-day war, it can often still be very hard to assess them accurately. There's a lot of luck involved in fighting, even if you know what you're doing tactically.
I wasn't involved in the war planning in any great detail, so feel ill-equipped to comment on how each alliance fared as a whole.
Oddly, I fought one of my TOP opponents in the noCB War for MK when he was at TORN.