Really difficult question, I think you may first need to consider which operating system you prefer ios or android. Both have some great features but ios is probably the most user friendly but for that you lose some flexibilty and customization (iPhone is also going to be more expensive).
I'm writting my response on an HTC one and I really like it, I enjoy the android operating system but I did find it a bit hard to get used to at first. The HTC has brilliant battery life, nice screen, is fast enough for everything I need and I can get loads of apps I want /NEED! On the negative the keyboard is small and fiddly (though I could change it with another apps, which you couldn't with iPhone) and I don't much like the download manager to synch stuff between my computer and the phone.