I think it's Bitcoin at this moment because its price has grown so big that the minimum wager I need to make is somewhat small enough. Having a small minimum wager is important to me because I don't like the risk, I usually think of strategies and those strategies would require a lot of money just to touch the "safe" streaks. Maybe Etherum is my next favourite currency, its price is high enough to have a "reasonable" mini wager but it's low enough for me to buy a large amount of it.