Tub surrounds: cost vs durability

[Christopher B.]

I've searched every keyword(s) possible here at BP and while finding some info I wanted to get more insight. If there has already been a discussion that I didn't find feel free to post a link for me.

My duplex was built in 1951 so I chose to leave the cast iron tubs and refinish them. Currently I have a cheaper 3-piece tub surround in each unit but I'm having issues with the caulk peeling off and it's very suspect to mildew and growing some mold. I live in 1 side and rent the other, we both maintain clean homes and the bathrooms are vented so I'm not sure whats causing the problem.

Since I am about to do my 3rd re-caulk in as many years in my bathroom my question, for this property and future rentals, is what have you found to be the most durable and cost effective route for tub surrounds?

I can get nice tile fairly cheap if that's the best option. I've also read some posts here at BP touting cultured marble. I'm open to anything and am willing to pay more now, within reason, for more durability and less maintenance long-term.

Suggestions?