Got the other side cut tonight:
I used the plasma cutter tonight. The cutting process took a little less time and I think its the safer way to go. Using the cut off wheel to make the vertical cuts felt like the wheel could grab hold at any point and try to kick back into your face or arm at any time. No worries like that with the plasma. I think I was able to make a nicer/straighter cut with the cut off wheel though. Overall though, I don't think either method is better or worse. I will be dressing both cuts with a grinder to get a good bevel on them before I weld them up. I may also have to do a little more trimming/grinding to get everything square, straight, and level.
Oh yeah, the plasma is definitely more fun!