In the world of e-sports, it's always a hot debate as to which game dominates at the pro level. From my research, it seems that Dota 2 currently holds the title for the biggest e-sport, mainly due to its incredibly high prize pools and large fan base. However, it's closely followed by other popular titles like League of Legends, Counter-Strike: Global Offensive, and Fortnite. It's worth mentioning that these rankings can change over time as new games emerge and the e-sports landscape evolves. In the end, the biggest e-sport at the pro level may vary depending on one's personal preferences and regional popularity.