If you are restoring, it becomes a matter of taste. Reproduction parts are slightly more available than GMC parts. But if you start out with a sound truck it won't matter.
It sounds like you are just starting a family, I would think about the future in your choice of vehicle too. My choice would be the 7 passenger suburban, but then I am biased too. I like the GMC, many don't. Values are about the same and once you walk away from the grille, you can hardly tell the difference.
The engines are different, the GMC'S have always had the full pressure engine, with sizes of 228, 248, or improved with a 270 and 302 to power your truck. Chevrolet did not have a full pressure system until (I think) 1954, they were powered by a 216, 235 and the 261 can be installed too.
The 1947/50 have knee action shocks and slightly less seat room and the 1951/53 were a little more roomier and had improved braking and suspension (tube shocks) The 1954/55 trucks were improved with a one piece windshield, full pressure engine and a different dash. This is where Chevrolet and GMC really differ.
Look in the gallery for the different looks that these trucks offer. Use the search feature to discover past posts regarding any questions that you may have and most of all......welcome!
