In my humble opinion, as a paid-up "donor" to PocketFMS..
Garmin is miles better than PocketPC + PocketFMS. Hands down, I'd take my Garmin Pilot III any day despite its smaller screen and lack of colour. PFMS is just too flaky, unreliable, slow and annoying to use. The Garmins are dedicated and do the job really well.
On the other hand PFMS is cheaper if you already have a suitable palmtop.