I have Op/Tech Pro Loop Straps on both my DSLRs. I wouldn't trade 'em for anything.
The advantage of the loop straps is that they more easily fall to the side when not in use and are probably a little easier to attach. The non-loop version has more height adjustment but the straps apparently are more likely to be in the way when you handhold the camera. I did a little research before buying the second strap and it sounds like those who has used both prefer the loop, that's why I bought the second one that way also.