We are about to redo the damaged subfloor, floor, and bathroom on our second floor. We are debating fiberglass which flexes easily and doesn't seem to mildew or mold as quickly as tile. Versus tile which looks better but seems to break, or pop out of the mortar as our house has moved/settled (which ruined our tile entry way) after the last earthquake. The code in our area for second floors allows a huge amount of spring to the floor. (Enough that when the re-plumbing was done, I could literally watch the floor bounce up and down in the shower and the bathroom as the 200 lb. plumber walked around. )

My questions for you folks are:
1. Is there a reasonable way to keep tile from cracking its grout, and popping loose on a bouncy second floor?- we will be replacing the plywood, but not moving or adding to the existing joist system.
2. Will fiberglass mold less than the grout lines on tile?
Thanks in advance for your input.
Doc R