Captain America, although there is room for debate for this one. It depends on the situation and whether or not either party has an edge with gadgets or outside information. Bruce could easily take Steve down if there was a plan from the start, and he had the upper hand. However, if we're strictly going with hand to hand combat, Steve has better endurance and durability compared to Bruce.
Okay, my turn... Let's get some magical characters up in here! Who would win Zatanna Zatara or Wanda Maximoff?