SpectreCoin, hands down. It's got high quality privacy technology to back it up, and more on the way. It's got an active and vibrant community that pulls together to help things get done. It's less than $4 at time of writing and currently has a very small market cap (and coin supply) compared to the other major privacy coins on the market right now. If the coin's market cap increased by 10x it would still be at least half the total market cap of most of the other major privacy coins (and it would be valued at about $40/coin). As time goes forward, quality privacy coins are going to be in greater and greater demand thanks to government regulation of the marketplace as well as taxation and even devaluation of government currencies (such as through central bank policies of inflation).

You can find out more about SpectreCoin by visiting the CoinWiki (in my signature), or by going to the project's Slack channel (it's quite active with helpful members and a lead developer that is very responsive to inquiries).
Slack Channel:   https://spectreproject.slack.com