I've done the GAP + C&O a few times (just did it this week). I've gone both ways. I prefer towards Pittsburgh. If you are only doing the GAP and starting fresh in Cumberland, you climb for 1/2 the first day and then you are done. There is not much significant to stop for and visit on the way up the hill unless you want to visit Frostburg and it has its own VERY steep but short climb. On the trail closer to the divide is the mason-dixon line, an overlook with a great view (best wide angle view the trail offers in my opinion), and big savage tunnel. All within a few miles of each other and all right there on the trail itself with no detour required, you can't avoid those sites even if you wanted to.
I will say on average if wind is present, it will most likely be a slight headwind from the divide to Pittsburgh. Either way, I still like that direction better. It is nice going towards Cumberland and having that 20+ mile down hill though. It all evens out.
Someone mentioned Ohioplye being busy. YES. No joke there. The lines for food and things and the people meandering around resembles an amusement park atmosphere. Most businesses and people are right there where the trail passes and it is jammed up, it's nuts. The GAP in that area is also walkers prime trail for getting over the river too. Unless you want to stop there and go down close to the river and rapids for a close-up, I'd simply carefully just pass though there. Sucks because there is a nice waterfall on a footpath you can go under and walk right through about a 1/2 mile down the road but just too crowded on holidays. Nothing else there that you would see you haven't seen during your GAP ride in other places. I'd restock or eat before or after Ohioplye. I'd suggest Confluence which has a grocery store, resturants, and a Dollar General less than 1/2 mile from the trail and without any significant elevation change.