i am no longer running a 486 but i have in the past
slackware 10 works quite well with it.
dont install X unless you really neeed it as it will be slow.
(if you have enough HDD to do so (i only had 800MB))
if you do use X then use either cholestrol free DE (XFCE)
or *box (black box, fluxbox, hacked box etc...)