As others have stated, take your time! There is so much to see and absorb, you really don't want to rush. If someone goes with you make certain they are a baseball fan, my wife would tolerate it but not as long as I would wish.
As far as a favorite, I would have to go with something rather obscure, the corrected picture and story of Art Shamsky hitting 4 consecutive homers along with his bat. When I visited there for the first time, I noticed that they had Shamsky listed and pictured as a Met, he completed his feat while a member of the Reds. I wrote the Hall a letter and sure enough they corrected it and sent me a nice letter thanking me. It feels good to know that I had a very small impact on the Hall of Fame
Enjoy your trip!
RC