Adventurer is right on--that's why I said I would have easily picked Fruita up until a couple years ago, but Moab has added so much since, and he didn't even mention my personal fave of the new, Deadman's Ridge, part of the new additions to the Brands Trails area or Dead Horse State Park, which is novice friendly but also crazy good fun for an advanced rider.
I loooooves me some PBR at 18 Road/Fruita, but that's just a couple miles compared to all the new stuff Moab has added.
But then again, all this talk about new stuff is pretty irrelevant--both places have far more than you could ride in a single trip, so don't sweat that.
I'm also a Springs guy and I'll definitely ditto your Blackjack experience. I ride the the black trails at Palmer Park and my fave on my end of town (SW) is the technical descent down Section 16, but nothing put the fear in me like Blackjack!
If you want a Blackjack-like experience that doesn't threaten to maim you and has really sweet flow, hit the Lunch Loops area between Grand Junction and Fruita and do Holy Cross--I've never heard an advanced rider not put that in at least his/her top 5.
But wait--you're a Springs guy--you definitely live close enough to hit both of these destinations without too much expenditure. Flip a coin and have a ball--then go back to the other at the earliest opportunity.
Besides, deciding which one to go to is just the start. Then you'll have to ask which specific trails to ride at your choice, and answering that won't be any easier!