Which compression format that comes with Stuffit Deluxe is the best. Best meaning it compresses the most, regardless of how long it takes. I ran my own little quick test with a single file and GZip was the best, followed by Sit and Zip, though i forget the order, than Unix Compress was really bad compared to them. I always liked GZip anyway, and I usually tar and gzip my files as opposed to stuffing them anyway. But now it seems gzipping really is the best way to compress a file.
Of coarse the killer of Stuffit right now is the fact that the finder contextual menus let you stuff files easy, but totally lock up the finder system 7 style until its done.