What are you using the drive for? playing games, Audio or just installing?
My 486 got a new (or 2nd hand) drive about once a year back in the day but that's settled down now with large hard drives, where you can no-cd games, network, to copy files or entire game install form other pc's. The only thing I haven't found a solution for is games that use CD Audio for music.
That said Plextor was the big name back then, but any IDE drive will be getting on a bit now. I'd get whatever is a good price, faster drives aren't going to help much in a 486, in fact you have to wait for the stupid thing to spin up and down.