I'd buy an iPhone 4 now.the phone that lasted through everything... finally took its final tumble and it's done.
Then you will be more likely to be eligible for the iPhone 6 which is really going to be the one to have.
No matter if the next one ends of being the 4S or 5, it will be the last year before the big rollout of the A6 chip and the new combined OS. That's going to make a huge difference and will take maximum advantage of a well sorted out iCloud as well as the newer apps and software.
I have an iPhone 4, and have had every iPhone before it.
Yet I'm taking a pass on the iPhone 4S or 5, as I simply don't see any good reason to buy one. No matter what it has, it's not going to matter. A major upgrade like the A6 and new OS will be a super upgrade.
One I will definitely buy.