For those of you thinking of taking up the free trial then do it via Quidco if you have an account. They are currently offering £5 for any new trial sign ups and a further £15 if you then become a member, pays for the first 4 months of membership. There is a similar offer for lovefilm too.
I have Netflix and LOVEFiLM but don't watch a great deal of TV so from my own point of view neither is worth the money.
However from my own personal experience LOVEFiLM is better for films and Netflix is better for TV. I've tricked my Apple TV into thinking it's in the States and the US netflix has allot more content than the UK one.
I think if you are the sort of person that sits down and watches DVDs then I expect they are both great and well worth the pittance they cost.