First and foremost I need the clasp be comfortable to wear and easy to operate. If it irritates the skin my neck, or if it's such a nuisance to operate that I find myself not wearing the necklace, I restring the necklace with a better clasp.
I also prefer that a clasp "go with" the overall appearance of the necklace.
I would not pay a lot for a clasp, personally. And I realize that it's harder to avoid doing that, now that gold is so dear.