What's the best solution in terms of your eventual product? Replacement, of course. But when other factors are added, your thoughts about replacement might change. Here's why:
The cost of the new bathtub is only the beginning. Visit a home improvement store, and you will find cheap tubs. Currently, you can get a standard 5 ft. Porcelain enamel metal tub for $134. But add in the cost of a contractor, demolition, removal, landfill fees, tilers, and a plumber, and the total cost of the job has ballooned.
Relining a tub is pricey, and it merely covers up the problem. At prices equal to or greater than refinishing, bathtub liners are not the bargain option.
You can install an acrylic liner, but it is still costly, and it only covers up your bathroom problems. Compared to all that, refinishing your tub looks pretty good.