I am not an expert on this but just sharing my own humble opinion. The way I am seeing is that both projects (one with 5 million and the other with 10 million supply of coins) can be doing well since they are both having a small number of possible coins...that is based on the fact that there both deflationary in nature. Now, if I were you, I would concentrate on looking at the potential of both coins in the market because in this case the supply will not matters a lot since they are actually small. A good project that can be getting a good adoption will be more valuable even if it would have x2 coins in terms of supply. So am concluding by saying that why not get into them both? Remember that you must make sure to put your eggs not in a single basket, anyway!