Obvies from Android: Samsung S4 (not yet released, S3 is just fine) or the HTC One (seems to be cool).
Galaxy phones are pretty top of the line, they have great features and are reliable. Battery life could be better, but Samsung offers a larger battery (mAh) in the same space (no ugly battery extenders). HTC One is HTC's new device which is kinda nice looking, and has similar features to SGSIV. HTC was once the leader in Android phones, but has since been seconded by Samsung (#1) - either way, they know their stuff and make great phones.
With all android phones: root and custom rom ASAP. Pay for the hardware, not the bloat and shit interfaces they shove down your throat. (this is just my opinion; see: Cyanogen Mod or AKOP).
Else
iPhone