Which unlocked 4G phone with decent Camera?

[Du1point8]

Looking for a replacement for my ageing iPhone 4.

Its locked to EE/Orange and the sim deal Im looking at is Three unlimited data and 600mins/unlimited talk for £20-25 per month.

I want the high data for setting up a wifi hotspot for my iPad for work as well as travel so thats the main reason for 4G.

Camera is always good for those moments I don't have my DSLR around, so the better it is the happier I am.

Phone... thats the issue, Im not sure what to get?

iPhone 5s/6 maybe as I can sync with the macbook and it just works, but then how often will I do that? Will the old apps work on my iPhone 4 without the sim working as there are a few I want to keep but only seem to be on iOS.

Is there any other phones that are out there that are good for my requirements?

Would prefer iOS/Android.

I need to port my number so I assume this is doable with Three? Are there any better deals out that the one I listed?

Ideally I want to keep the next one for 4 years again so need it to be not just about to be replaced/discontinued.

Help...