Your best bet is usually to keep a cast iron tub as they are so superior to the steel and plastic tubs used today that any comparison is rather funny. The old tubs hold heat much bettere than steel and plastic tubs serve most to make hot water cold. Reglazing is the way to go but be careful with your choice of installer. DON'T let anyone spray epoxy!!! This is an industrial coating that has no place in the home. Almost all epoxies use polyisocyanate hardeners and this stuff is dangerous. Aside form the health harards, epoxy goes yellow, turns dull within months, and is prone to staining, for a start. You should use a polyester-urethane material that is iso-free. These can be applied much thicker than acrylic compounds and have superior aesthetic characteristics. Be sure your installer properly cleans and preps the surface, removes the caulk line between the tub and wall completely, and removes the overflow and crossbar, and, very importantly, removes the strainer (drain). This last step is the sign of a pro as the cowboys don't want to be bothered with this last step. Strainers spin out reasonably easily if you have the right tools (and sometimes a heat gun). The installer should return after the tub has cured and replace all caulking, gaskets, and fittings. I "shoot" tubs for a living and the above points come from experience gained over more than 1,000 jobs. Good Luck with your project!!