Think about which you would use more and for what reasons since they are from 2 different plaines.
I've owned both, 1 GP100 and going on 7 1911s.
Don't believe the people that say 1911s need to be tweeked and repaired and blah blah blah to be reliable or accurate. 1911s are some of the most accurate guns out there and out of all 7 of my 1911s not one has ever had a single failure in 3/3 1/2" & 5" models. The 1911 brands I've owned are, Kimber, Springfield Armory, Taurus, Regent and Rock Island Armory. Get good mags like Wilson Combat, Kimpro Tac mags or even Act mags from Wolff with their extra power mag springs in them and your GTG.
Rock Island Armory has a lifetime warranty btw with excellent customer service but I'm sure you won't need to use it.
My GP100 was also 100% reliable and very accurate. I had the 6" Stainless version with adjustable rear sight. Everyone I knew wanted to shoot it. The only thing I changed was the grips for some finger grooved/palm swell Hogues.
You can't go wrong with either one, so just figure out which one you think your going to use more for what purpose and go from there. IMO though, everyone should have at least one 1911. Which ever you get, clean it up before taking it to the range, lube properly and be safe and have fun.