The "best" watches for serious collectors are the ones with low production runs. The problem there is that Rolex doesn't release production figures on a per-model basis. In fact, it's (not impossible, but) hard to even figure out their over-all production numbers.
Nobody can forecast which Rolexes will drastically increase in value. If we could do that, we wouldn't have to work for a living! The best way I can think of is to buy gold watches and wait for the bullion value to hit $2,000/ounce. :laugh:
For vintage watches, it would help to know what your colloquial definition of "vintage"is. The best places to look are the big name auction houses like Sotheby's, Christies, Ashford, etc. If those places are too much for your budget, or you're not looking for something from the 1930s, 40s, or 50s. hit the watch collector's websites that eschew the ownership of counterfeit watches, and have sales pages or sales forums. The members are pretty knowledgeable about what they have, and know how to take proper care of their watches. It's not a perfect solution, but it sure beats trying to read between the lines on those offered on eBay.