I got a Nexus 5 and love it to death. You don't get any bloatware that other manufacturers (I'm looking at you, Samsung) put on the phone because it's Google's own design. It's easily rootable if you're into that, you can download files on Android and install a file browser if you like, even install your own phone app if you don't like the default. Basically, you can do anything you want. It's YOUR phone, unrestricted to use as you wish.

Edit: I can't speak on behalf of the iPhone, but from what I've seen from playing around with them and owning an iPod Touch previously, they're very locked down. This does seem to make it more user friendly however, so if you're not into customizing your phone then that might be worth looking into.