For me, it's SKY by a reasonable margin.
Not to say they aren't perfect, I prefer DC's ability to doorstop a bit better in grid-walks, the fact it's the BBC I think has more sway in some conditions, and I do slightly prefer Jake over Simon for anchor, but for just about everything else, SKY have it, notably for..
1. All practise sessions seamlessly series link in the planner
2. The commentary in practise sessions is good, with Ted doing his walk abouts while you get decent commentary from Ant Davidson or Alan McNish when he's not there
3. The Sky PAD and virtual Eye etc are all quite good, plenty of post race analysis
4. The off bit of the Sky F1 Show adds to the build up.
5. 5.1 surround does sound pretty decent, not for the surround aspect, but just the audio quality in general.
I really like Ted's doggedness in getting good info, and Crofty/Brundle make for a good pairing IMO..
Last year with the BBC, I was often using 5 lives commentary and missing practice sessions, and not feeling much going on outside of the race (no 'F1 Show' kind of thing)
I would say that you get used to the different personalities, I've watched 75% SKY and 25% BBC this year (due to being away from home) and everytime I watch 2-3 races on one channel, then go back to the other, it always feels weird..