Like ByTor said, don't expect massive gains nor expect to flip it soon for any profit. Considering that Rolex has had 2 price increases this year alone plus rumors of another one coming soon also, you would be safe with any of those ByTor already suggested. I would advice getting a sub, gmt, or sd pre-owned in good condition with box and papers. After a decade or FEW u would easily get back what you paid AT LEAST. Some WIS's are considering getting a NIB "m" serial GMT-IIc and keeping it in new unworn condition for a few decades with the hopes it would pay off with a higher that average resale value. I don't know if you are a gambling person or not, but it seems like too many "if's" in this equation for me...
Personally speaking - I have my gens, I wear them, enjoy them, and feel comforted by the fact that I know I will at least get back my initial investment if/when I wanted or needed to. I'd rather buy the watch for wearing and enjoying rather than an investment (..even though all my other investments have been goin to "heck" lately, yet Rolex is raising prices non stop... :-) ). Just my 2cent :-)