Well, I am a GPS junkie and a sucker for new tech. Garmin is my unit of choice due to my experience flying in Alaska - they are the go to company for serious aerial navigation. I have, lately, come to think that an entirely different division of Garmin makes up the handhelds - it just seems so different...
I have had the Colorado and most recently the Oregon. They are VERY COOL units - awesome displays and pretty easy to use - the Oregon being touch screen trumps the Colorado's wheel control. They feel good in your hand and of very high quality. The drawbacks for both are very short battery life, long satellite acquisition times, screens that hard to see outside, and generally difficult to use quickly and easily. Forget about cold weather - the batteries will poop out ASAP and gloves make them difficult or impossible to use.
So, my old stand by GPS is the 60CSx. It is not sexy, has a small screen and lump for an antenna. However, it quickly picks up sat. signals, holds reception even in thick cover, is easily read in any light and can be navigated with gloves. It has a Micro SC slot and I have used the TOPO of course and the City Navigator guided me from Anchorage to Seattle to Denver with ease.
I also have a NUVI 255W that stays mounted in the car. It is handy for getting around town, but I trust the 60CSx for trail / camping / location work.
