Sims will prefer the shower over taking a bath in most cases. The bubble bath will only be chosen autonomously by kids, goofballs, childish an pregnant Sims. The special baths that came with Spa Day are reserved to be autonomously chosen at the relaxation center and will no longer be chosen by your party guests and other visitors.
This is the cheatiest mod I've ever made but I needed it when playtesting some other mods. What it does it fairly simple: it helps to complete your sims' daily task while helping them skill up in the skills and/or requirements needed for promotions and performance.