Good older iphone/smart phone model?

I'm looking for a new phone, but I'm not sure what to get. I'm looking for an iphone or smart phone but I'm on a deffinate (up to about £70 or so) so I was thinking of buying one of the older models used. I want one that I can use for: going on the internet, reading manga and preferably snapchat, but otherwise I don't mind. Also, any tips for buying them second hand and what to look for when buying would be welcome.

I don't think you'll find any good iPhone under 70 quids. You can get the iPhone 4 new in that budget but it isn't decent enough for heavier tasking. If you really want a decent performing iPhone, you should get the iPhone 4S which you can find used but raising that budget a bit can get you a minty iPhone 4S. Other smartphones if not iPhone will be Lumia 635, Samsung Galaxy S3 Mini, Moto E, Lenovo A916, etc. If you need help with getting one decent smartphone in your budget and at reasonable price, mail me for more info.