That's a tough one. Both are a little long in the tooth. I'd bet, though, that there are and will continue to be more Lear 35's running around for a few years than Falcon 20's, making the Lear type more useful for a longer period of time.

Those Falcon 20's are tough to resist, though, especially the re-engined, re-cockpitted ones.

Which one pays more right now? Which one offers the quicker upgrade (if starting as SIC)?