i'm currently using a Knog NERD. doesn't have heart rate or cadence, so i want to upgrade.

Polar CS500, comes with the wearlink strap and cadence.

Garmin. GPS, but tiny display.

and then there's the vaporous PedalBrain.
uses the iPhone, so that's one fewer device to carry.
adds a battery to the iphone.
biggest screen, most familiar interface maps
BUT - god knows when it's coming out, and the iPhone would be exposed to the elements/crashes, and there are no physical buttons.

so, what would you go with? is the GPS a compelling enough feature to go with a Garmin?