While there is no "always true" answer to this question, most people prefer using acrylic paints rather than enamel. The main reason is that many people have found that the enamel paint will remain "tacky" on a Stikfas figure for much longer than it does on other models and plastics. Sometimes it takes several days to completely dry, while acrylic paints usually take a few hours at most. However, enamel paints will dry much harder than acrylic paints, which keeps scratching and chipping to a minimum even without a protective coating added.
Not everyone has this problem with enamel paints, and it may be due to the brand of paint. Most Testors enamel paints will remain tacky for a long time. Also, adding a spray acrylic clear coat to enamel paints will sometimes cause the paint to re-liquify again. It appears to happen with metallic flake Testors enamel paints most often. Some paints and clear coats warn about the same issue.
