It all depends. For airsoft, most gun shoot about the same so there is no real gain in distance, accuracy etc.
What it all boils down to is your own preferences. What role do you for see yourself fulfilling in the field. Do you want to imitate a bad guy, a specific unit or maybe no preference at all? What kind of things do you want out of a gun regarding to looks, functionality of use in the situation to be used in, mag compatibility with other players, gear compatibility, ability for attachments and add-ons, battery type and size of the battery storage area. These are a few things to consider and only you can answer those questions for yourself. By doing so you will have a good base to start from and will narrow down your search.
It's not as simple as do I want a red one or a green one :lol: