If you have an iPhone, the quadlock is tough to beat.

I have an Android, and I would say I'm an ardent supporter of the Delta Smartphone Caddy II due to the differing sizes of various Android phones. When it comes to universal mounts, it's without question the best combination of support (it wraps around every edge of the phone) and ease of use/ingress/egress (takes me 1-2 seconds to put in or take out my phone). RAM Mounts are bulletproof mounts, and they're great in automobiles, but I still swear by the Delta.