Unfortunately, privacy coins are a very niche market.
Actually, normal blockchain technology is fairly anonymous already, so those who want ultimate privacy are really looking for specific use cases.
Of course, the first things that spring to mind are all unsavory transactions: contraband, illegal goods, tax evasion, etc.
But not all use privacy coins for these things.

With that being said, I believe that monero is the best privacy coin out of all of them.
Dash has a higher market cap, but it is highly plagued by questionable development and acts.
There are coins out there with some really impressive features, like cloak coin, but monero has the ultimate benefit of being an established company with a trusted product.

With all of this in mind, I believe that monero still has a lot of room to grow.
The last couple of months it stabalized around 90 to $100, now, when the prices stabalize again I think it will keep above $100, then shoot towards $200 in the next bull run.