Android? Galaxy Nexus? Sprint? Or not?

First smartphone here. Being the somewhat security-conscious guy that I am, I used to more or less despise the Android platform, for its security issues. (I understand that the Android OS itself is no slouch when it comes to security, but the lack of vetting in the Android Market, and many known cases of malware turned me off.) However, if I go iPhone, I won't be able to take matters into my own hands at all. I won't be able to hack around. I want to be able to do that. It seems that if I'm careful I should be fine on Android. I like the idea of being able to flash Ubuntu Phone, Firefox OS, or anything else to my phone if I want to. I also want a mobile Bitcoin Wallet. No joy with Apple. I know the Galaxy Nexus is old, but that makes it an inexpensive phone to buy outright, and I'd think it's one of the most hackable phones I can get. But I want your suggestions. Is there something else I should be considering?

And yes, budget is a big issue. I'm looking to buy used. On that note, I'm thinking I'll buy a Sprint phone and start out on Ting. AT&T doesn't have LTE coverage where I live. No LTE on Verizon except on contract, and that's too expensive. T-Mobile sucks here I'm told. I know Sprint is slower than Verizon or AT&T, but given my situation, do you think it's my best option?

Yeah, I've pretty much settled on a used Galaxy Nexus for Sprint, but I want to run it past you Vergerous Ones, in case I'm missing something.