Which I phone?
What are the main criteria in choosing an iPhone?
iPhone 4, iOS 10.2.1, iPad & 27" Mac
That is completely up to you.
To some folks, a high quality camera is important.
To some folks, processor speed is important.
To some folks, available storage on the iPhone is important.
To some folks, price is important.
These are just some examples of criteria. Yours may be different, or match some or all the above.