I think overall, I've played in as many or more one-shots than campaigns, though not by preference.
For the first few years I was playing D&D (just occasionally, off and on) with my high school buddies, they just ran one-shot sessions or short adventures of a few sessions in length (the longest 'campaign' I played in at the time was probably 5-6 sessions, if even that long). This was with 2nd Edition AD&D mostly, I only got to play about two sessions or so of 3rd Edition with my friends.
After I had to move to Arizona with my parents, I came across WebRPG and then OpenRPG, starting to use the latter and join campaigns. I finally got to start playing in prolonged campaigns, starting with Emiricol's Bandora homebrew D&D campaign. Since then I've played in a handful of year-long, half-year, and two-year campaigns (maybe one three-year campaign). I've also played in a few one-shots, since various campaigns I joined had died shortly after starting (the DMs never really gave a reason in most cases; I and the other online players simply lost contact with them at some point).
Mainly I've been DMing though. Only a single one-shot, and about six campaigns I think (two or three of which have just been half a year or less, aborted when scheduling problems with the players became too numerous); technically one was just me substitute-DMing for Emiricol, in the For More Than Glory campaign of T13K, briefly. And technically, I think the D20 Modern: Agents of Psi campaign I started last week counts as my seventh campaign, though I dunno how long it'll stay together (playing with folks at the local gamestore, whom I'm not especially familiar with yet).