Lots of people still play WarCraft III. StarCraft II isn't necessarily better than WarCraft III. It's just different.
However, I also advise making single-player games. While there are still many people playing online, the multiplayer scene has been dominated by bots who rehost the same games over and over, preventing players from finding newly-started ones. As such, it is very very diffictult to promote a new multiplayer map on battle.net these days.