i swear by (and very rarely at) my original tom tom go. most of the big gps names use the mapping data from one of 2 companies and it's the mapping data which can make or break a product so they are all pretty much of a muchness.
of the bunch i'd either go for the new tom tom one or a go 500 dependant on what facilities i needed.
i'd not touch a pda, phone or notebook based system, they sound good in theory but are often slow (phone), can have compatibility issues with other software (pda) or are dangerous (an unsecured notebook in an accident?). the latter do tend to get updated more often though which may make them worth it if you don;t mind the hassle.