Don't just buy the latest model, especially if you really don't need the extra features it offers.
But if you love listening to music, get a model with great sounds. Make sure to read reviews because even 'higher' models are not necessarily better.
If you're a blogger who loves documenting things, get a phone that's high on resolution.
If an exercise buff, get something with a pedometer.
If you love travelling or are into outdoor sports like climbing or cycling, get something with GPS.
If working on the go, get a PDA phone.
This way, you minimize the gadgets you do have to always have with you, not to mention the kind of memory and accessories you'll invest in. It would also be one less charger to find.
What if you want all those things in one phone? I think that's possible and there may be already something like it in existence, but do remember that if you insist on everything, something's got to give. PDA phones are slightly bulkier, for example, and won't really be handy for the outdoorsy type.