As someone who own's a 15-22, the umarex colt and the ISSC SCAR I do believe the 15-22 is slightly more accurate the the other two. However each one has its strong points. The 15-22 functions like the real AR. The Colt looks almost identical and the SCAR looks almost like the original and for my personal preference is the '"baddest" of all three. The 15-22 seems to shoot anything you put in it without problem. The SCAR is very particular and likes CCI. Hope this helps.
Life member NRA