The folks here always seem to get it right...

This is something I am pretty up on and Garmin and TomTom really are the hot two brands right now. But as always these things change over time.

TomTom has better, more intuitive software by and large. Not surprising given their beginnings as a software company for other makers.

Garmin's strength is the hardware side of the product and the various cofigurations that go with that (portable, mobile, etc).

Easy answer?
If you want tougher, more flexible hardware options that you can walk around with - go with Garmin.

If you are going to mount it in the car - Go with TomTom.

Good luck, you can't go wrong with either.