Full sized stroller is great if you also want to have the underneath storage convenience. Yes, it's bulky on the bus and you will usually be asked to place it under the seats, so it needs to be able to fold all the way.
Once you're in the park, it's great to have and worth the struggle of the bus.
Umbrella stroller... much lighter, but no storage for snackies and stuff.
You'll probably be fine no matter which you take...