In reply to Eann:
Went round this loop when my S2 suddenly died last month. Considered getting a replacement from eBay, but decided it was time for an upgrade.
Nearly got the S6, but ended up paying a bit more for an Xperia Z5 as much newer, better battery life and waterproof and, importantly, can take micro SD cards to increase the memory, which the S6 doesn't. Looked in 2/3 shops and nearly every member of staff I spoke to had a Z5. Also has the best camera on the market, although not really a selling point for me.
Taken a bit of getting used to, but that's as much the change in the Android OS as Sony's skin compared to Samsung's. There are still a couple of things that annoy me, but a couple of other things I really like.
Still getting used to the size - sometimes think I should have gone for the compact version and sacrificed a bit of spec.
Functionally, it's much faster than my S2 - things like the sat nav app are much smoother (and better on the bigger screen).
PS: get the Tech21 case from the O2 shop.
Post edited at 13:03