Welcome to iMore! Not a lot info to provide you with an informed answer. My first and foremost suggestion is go to an Apple Store and try them. It really comes down to a personal preference. They are all capable of do a good job for you, be it the 5s, 6s or 6s Plus. You may even want to wait till the introduction of the 5se before making a decision. It really comes down to what you like.
It depends on how much you want to spend-
Personally I keep up w the latest iPhones and sell them pristine when the new ones come out owing very little-& placing the funds towards the new phone.
My only recommendation is get 64g at the least.