Should I upgrade my iPhone to 5s or 6?

Should I just go with the 5s cause it's less expensive and just as good? Or is the s6 what I should be getting? I
currently have a iPhone 4

Upgrade to 6 or 6+ … Or wait for the new IPhone on September…

I'd get the 6, but if you would rather wait for the 6s which is expected in September then it may be the better bet. Would have the same price as the 6 does now.

I don't know why anyone would use 4 today with 5C free on contract, so I would at least do that. If you want the bigger screen get 6, and 5S is a good deal at $50 on contract.