in my opinion, check groupon and google for coupons before you make your choice.

Depends on your flexibility. If you are flexible you could risk just walking in the day of or if you have plans I would suggest buying them ahead of time. We were able to walk in the day of and only waited about twenty minutes (which we spent easily in the gift shop) but I hear it can be very busy at times.

I'd get ticket before. We did not get our first choice of tour times when we got there and had to wait about and hour between tours...