Sky offers several sports as well as movie channels, plus extras like Sky Atlantic. Sky's sports and film channels are also available on BT. Sky focuses on sports in terms of its own in-home channels, with rights to some Premier League matches and all Champions League games. In my opinion, Sky is the best choice.
I have both, to be fair BT TV offers me almost all of whatI need for myself and for the kids, my BT TV is also a lot cheaper despite me having a decent discount on my Sky package.
BT TV is missing the likes of Sky One, Sky Atlantic, Fox and some others, an issue soon to be solved this year when NowTV is supported, I can see me ditching Sky then or once my contract ends, I don't watch any sports either, so that could be a factor if deciding.
I have sky and I know its a lot but I don't think BT TV is as good.. No sky sports, bad movie selection. I also am not a big fan of the interface but if you arn't particularly bothered about sports or movies I would probably give it a try..
I like the BT TV interface, it's easy enough to navigate, in terms of the response time I'd say it's as fast as my Sky Q which is a huge plus.
I had Virgin TV a while back, that was horrid, the colour was a an eye sore, is it still plum/purple/brownish/red ? and it lagged so bad, moving channel to channel or through catchup took forever.