Of the two I would select the eTrex Venture HC.
A selection with a little disclaimer. Gps manufactures have some quality control issues over the years. During the one year warranty period Garmin has been real good. Quality Control on the same model varies, some seemed to be bullet proof and others failed. I sent my eTrex Legend back to Garmin because the exterior rubber was coming lose, they sent me a replacement. The replacement has been doing good for ten years.
The metal battery contacts in my first 76Cx broke within the first year while under warranty. I used that unit almost daily, and I replaced rechargeable batteries daily. I believe that one of the issues is that as rechargeable batteries became more powerful the overall battery size increased put additional stress on the contacts. Garmin replaced in with another unit. I had that unit loaded with City Navigator software and Top software. Garmin set me up with a new lock code to open City Navigator in the replacement unit. The replacement 76Cx started having fade out issues when on battery powder. The issue was not repeated when hook to the 12v system in the PU or the computer. The second 76Cx had very little use because I was using my new Rino 530Cx(s)
Just after the eTrex Legend came a 76C I bought it because it floats, it has 115 MB of memory which I needed because of my on the job travelling. This unit has been a solid performer. I gave it to my middle brother when I up graded to the 76Cx.
I have used the 76C and the 76Cx on land and water. When out trolling I set on the stern of the boat using the kicker to troll. I can look forward at the fishfinder, and I mark fish on the 76C/76Cx. They are designed for marine use and float if they go overboard. I normally change rechargeable batteries in the afternoon. The units are on from when I leave home until I get back. Fifteen hours plus are normal.
The Rino 530Cx has been a real adventure, I had to return three to Garmin under warranty. The 3rd Rino 530Cx has worked great the last two hunting season.
Just before the 2011 hunting season I contacted Garmin support because the replacement 76Cx was fading out. It was hardly used because my focus had turned to the Rino. Garmin said I could return it and get a replacement for $117.00+. Knowing that I new unit would cost me much more I took the deal. After I received the new one Garmin gave me a new unlock code to use my City Navigator software.
Garmin has come out with some new models that sound interesting but I do not plan on buying. I have the two handheld units, two automotive units, and the fishfinder on my boat has a gps function.