Just as Icom in the personal VHF world leads the way Garmin and Delorme tend to lead in the GPS world. If you want both radio and GPS as stated above take a strong look at ICOM. If the GPS is most important stay with Garmin or Delorme. The new Delorme PN 40 is giving Garmin a run for their money. May I suggest you get them both in hand and determine which screen and button layout works best for you. The Garmin 60 series which has been out for several years without question sets the bar to which others are measured.
Go to gpsreview.net , groundspeak.com and you will find tons of reviews and post. For comparisons go to Garmin | Follow the leader
or Delorme.com and you can compare units side by side.
As far as Garmin units, it all comes down to button layout and features, color screen, electronic compass, topo or nav maps etc.... The Garmin 76 series although offerred as the "marine friendly series" just means it will float. The Garmin 60 and most are waterproof just don't float. Delorme only offers the PN20 and PN40. Battery life, customer service, dependability both Delorme and Garmin have it figured out.
The newest Garmins with touch screens, ie.. Colorado, Oregon units although top end units folks are still finding things that need to be worked out. May want to hold off on that series just yet..
Don't forget, which ever brand you go with you must also determine what software it requires and factor in map scale, charts, map features and cost. They tend to be proprietary.
PS you can often find last years version software cheap on line.. In most cases there is little change