None of them.
iPhone, always same iPone as from the start, just with minor updates, etc more antennas and more softwares.
Thou they're still very bad at fixing their bugs and performance eaters.
also I hate their way to make money, "OMG BUY iPhone 2 it's fucking awesome!!!!!!!" and few months later "Holy crap buy iPhone 3 we've changed it totally and is much better!!!!!!! <changed color is the biggest change>"
Samsung, their strong side isn't hardwares, bad performance together with lots of bugs on their systems.
Etc, send sms to someone = kill all process in the phone.. and so on.. lots of similar bugs that will freeze/kill the phone.
I'd recommend HTC, because their hardwares may not be the best, but it's working at all times.
Same with softwares, there's a few bugs on older versions, for sure minor ones on newer ones but you'll rarely face on, and when you do... just wait or restart the phone and you're fine to go again.
a huge recommendation, is that you get a DualCore, because with more processors, it can take more work, and the "bugs" will practically be gone together with it because of the speed it solves the issues.
Also, use a good operator that's fair, and that are better at making systems than making awesome commercial. (Looking at Swedish company called "3", their advertisement is a James Bond ripoff, great effects and shit, but when it comes to services.. connection timeout a few times each month, slow connections and no reception when you leave cities and run out over the country)
Nokia isn't that bad either, only their designs is, but HTC beat them in a fair fight.
If you ask an experienced phone-seller at a ware-house(unless he's a money-whore) he will say pretty much the same about me, he'd recommend you HTC because of their speed to solve bugs.
Oh.. I almost forgot, there's 2 bugs in Samsungs phones that has been known for almost 10 years... still not fixed... they're like cipsoft, it's better to ignore problems and just add everything else to make them look fancy.