How important is a grad school visit?
The decision is probably not that important, so don't stress too much (or, which is basically the same, it's pretty much impossible to figure out what the effect it will have).  Remember that this feels very high stakes for you but for the people on the other end, it's just another day at the office.  I would focus on which trip will get you valuable information.  In an ideal world, I would say go to school A for the weekend, and try to visit school B some other time, but I don't know how much of an issue the expense of the tickets is for you.  It would be a different matter if school B had admitted you; you might want to push them a little harder on getting details (have they admitted anyone).