I have no personal experience with Gymboree; but we go to My Gym in Columbia and love it. The amazing director at Columbia (Mr. Dan) is now at Owings Mills - so I can be pretty sure that facility is wonderful, too.
Another vote for My Gym...they're amazing! I haven't held or attended a party there but having been going weekly for months, I can imagine their parties are fabulous. The staff is amazing and I am sure they'd throw a wonderful party for your LO.
I have never been to a party at Gymboree but have been to one at My Gym and it was so excellent!! The staff was always there helping out, they brought the birthday boy out in a wagon and sang. The only issue is that the kids had to eat their food at the little cubbies and it didn't really leave room for their feet. Wish they had more of a party room for food.
Re: GYMBOREE VS MY GYM
lovelylittleworld
BFP#2 1/12/12 ~ Missed M/C 8w2d
Someone's getting a little brother!