Guess I'll play the contrarian here. Jackson has three obvious advantages -- he's clearly the better hitter, he's $400K cheaper and he's Shoeless Joe. But I have a weakness for those high speed, big range, Lance Johnson-type OF's. Mostil's 121 RC are pretty good for a guy who also gives you A+ range in CF, and he has a big speed advantage and a nice OBP edge on Jackson. Plus if Jackson shines for you, everyone will say "Of course," but if Mostil is a stud, everyone will say "Wow" and you'll get credit for a nice sleeper discovery.
Mostil by a half step... but maybe that's why you guys have so many more titles than I do.