Wow that's a highly, highly debateable statement there. Many people would say that the ACC is mediocre top to bottom. That's why all of the teams appear to be equally tough because they are equally average. They say the same thing about the Big East.
Miami is somewhat rebuilt, but is still just a shadow of its former days. FSU is getting more talent? Are they getting better coaching too? UNC is on the way up but still has a way to go. I mean the ACC rep against Louisville in the Orange Bowl 2 years ago was Wake Forest. WAKE FOREST! Seriously...
Of course it's debatable, but I think the best way is to look at how teams play out of conference non-bowl games. I'll exclude very top-tier wins/losses (i.e. Oklahoma, LSU losses, etc.) because we're talking about strength top-to-bottom, not just at the top.
Rutgers went against a major conference once last year - lost to Maryland at home. Louisville lost at Kentucky, but beat NC State. UConn beat Duke, but lost to Virginia. Pitt lost to Michigan State and Virginia. However, West Virginia beat Maryland and USF beat Auburn and North Carolina.
Clemson beat South Carolina. Florida State beat Colorado and Alabama, lost to Florida. GT lost to Georgia (and Georgia and Florida were both top 10 teams last year). Maryland's W's and L's were already talked about. Miami beat Texas A&M. UNC also lost to South Carolina. Wake Forest had a close loss against Nebraska but beat Vandy.
So it seems that the ACC lost most of its games against very top-tier programs, and SEC teams. The only quality OOC win I see from the Big East was USF over Auburn, but I see 3-4 quality OOC wins from the ACC, depending on whether you want to count FSU winning in Boulder.
These numbers change year to year I'm sure, I just think the ACC doesn't get enough credit for being strong top to bottom. People forget about the Virginia's and Maryland's that put up big wins each year, and the always solid teams like Clemson and Va Tech. Once Miami and FSU get going, we'll give the SEC a run for their money as the best conference. But that will probably be years away.