Phone to buy next, iPhone, Nexus?

Currently have an Xperia S although is starting to feel a bit old and am due an upgrade, although i'm going sim only next due to the cheaper cost and better data allowance which i need!

So will be buying a new phone, I don't want to spend anything over £200 so will be looking at a used but very good condition phone.

Id love a new iPhone but too expensive, a 4s might be just in budget but would rather not spend that much! Already have my ipod for music.

All i want in a phone is snapchat, instagram, twitter and a decent camera that isn't slow and dim witted like my xperia s at times, plus no lag if possible!

Is the nexus 4 my best bet, or just get an older iphone?

Added (1). To add, I don't want anything from the Samsung range! Don't get on with them.

Nexus 4 has a terrible camera apparently. I'd try get a second hand S3 or Note 1.

Nokia 3310