We actually did a ton of research on the buildings last year after we'd been so frustrated with the convention center by the end of Friday. I may be wrong in my recollection, but I believe we figured out that the larger building (north/south) had MUCH bigger meeting halls for panels but a smaller showroom floor. While the west building had a massive showroom floor, but very small panel rooms.
I also believe MegaCon didn't book the convention center soon enough, and the north/south building was claimed by the cheerleading convention/competitions at the time. IF I recall the research I did at the time, correctly. This may all be mixed up, lol. I believe this year they announced they'd be doing it at the north/south building, which I understand as those panel rooms are MASSIVE. Also no escalators if I remember, which made a huge difference in funneling people inside to buy tickets. If you're choosing a day to take it easy or a single day to go, I don't recommend Saturday unless there's a panel you want to see.
For reference, here was a view from the second floor of the entrance TO the escalators to go downstairs to buy tickets of MegaCon 2014. On Saturday, around noon.
I remember finding measurements and square footage of how big the showroom floor was for OCCC, but here's the north/south building from MegaCon 2013.
And then here is the showroom floor from MegaCon 2014. I specifically remember having more floorspace to walk through.