Head to head the single biggest difference I can see is that Ron Pierce tended to drive Roll With Joe with cover, he would invariably come off a helmet to do his thing...whereas I don't recall Mike Lachance driving Bettor's Delight that way. He was much more of a get into it early & mix it with them on the front end sort of horse & was driven accordingly.
I think Roll With Joe might have had a step or two more in the point to point speed category as opposed to Bettor's Delight and Roll With Joes a bit bigger and is different gaited too...but Bettor's Delight was most definitely a tougher racehorse all over, IMO.
Any examination of his race record now is kind of a moot point anyway.
Bettor's Delight already has the runs on the board as a sire & quite extensive runs they are, some $98,021,730 in total progeny earnings and counting. Sometime between now and the end of 2012 or very early 2013 he will top the $100,000,000 mark. Not bad.