Literally easiest way? Attila, Duel Map, Pangaea. Rush a couple of battering rams. Win by turn 50 most of the time.

Other than that, science victory, especially as Korea or Babylon. Go tall with 3-4 cities and beeline science techs (other than getting composite bows early to defend yourself). You can usually get to be a full tech era ahead of everyone else by the end of the game, depending on difficulty, which also means that it's really easy to defend against their pathetic troops. Depending on the map you might be able to win earlier with military or culture victories, but they're less consistent and require more effort.

If you don't want to choose a specific victory early on, Poland and Maya are good civ choices. Poland's ability is absolutely insane and adds up to a full policy tree by the end of the game, so if you do something you regret it's a lot easier to recover from or capitalize on it. Maya's bonuses are all very powerful as well: early archers, early science and faith, and a few free great people make for a very strong start to do whatever the hell you want.