I have both rifles and love them both but use them for different kinds of fun. The Colt/Umarex is for blasting lots of rounds and getting the AR15 feel for cheap. I've put thousands of trouble free rounds through it and my wife loved it so much she claimed it for her own. The 10/22 is for accuracy and plinking (although mine is all upgraded with Kidd parts).
If I was you and could afford both, I'd get the Colt from your friend now and the 10/22 later when you can find one.