I found opening day 2011 to be exceptionally busy, especially for opening day. Opening day in 2009 and 2010 were much more pleasant, with most rides (save Diamondback, BLSC, Firehawk, and FoF) reducing themselves to either walk-ons or something near it by the end of the day. I don't know what the draw was for opening day 2011, except that it might have had something to do with the later opening date. So, if that's the cause, TOPGUN1993's right--get ready for some pretty crazy lines.
I'll probably start KI's 2012 season with a ride on Adventure Express, as that's where I inevitably end up drifting first on most KI visits. With The Crypt gone and Beast's (in my opinion) less-than-pleasant smoothness record in 2011, AE's got significantly reduced competition for my attention. And man, I miss that Arrow mine train something awful. It's not absolutely crucial that I ride it first, but it's something I've got to hit up at sometime soon.
If I can't do AE, I'm not entirely sure that it matters to me what I do first. I'll firstly and mostly enjoy the fact that I'm outside at Kings Island (rather than in a gray classroom with entirely synthetic lighting) with friends doing what we love, and if that results in us riding coasters, so be it. Riding Adventure Express would be a cool start to the day, but it's being at KI with friends that I miss the most this off-season.