I've tried both and am currently using Lovefilm.
It has some newer-ish films such as Tinker Tailer Soldier Spy, Johah Hex, Inception and Despicable Me for example and I have really enjoyed watching 'Sons of Anarchy' for the first time.
I found both services to be pretty stable on my 3.5 Mbps connection but like Chopsen has mentioned, the picture on Lovefilm isn't as good, certainly on some shows which are terrible in places. I tried checking out the 90's X-Men cartoon and it's very compressed with lots of blocking/compression distortion etc. Other shows have looked fine so it's hard to say.
There's a fair amount of content on both services but I guess it depends on what you like. If you're in to Anime, Lovefilm is arse. A big fat empty one. Netflix has much more in that area and probably has more stuff overall.
Netflix was really easy to cancel. I think it was just a case of logging in and clicking a couple of things (can't honestly remember, but had no probs. I just get the odd invitation back via email every now and again).
If you decide to try lovefilm, sign up via this offer page
. If you continue using it as a paying customer (even for one month after trial) they'll send you a code for a £15 amazon voucher, so you're still a tenner up
Edited by Beetroot_Bertie at 00:56:47 02-02-2013