Range units (like archers) are the best against the AI, although catapults and warboats (galleys and quadrireme) can help you siege a city faster. Civilization VI is the first version of this series where the geography of your start location will influence your strategic choices. You will not go down the same used-up path everytime to get to certain techs because Eurekas! are very important to speed up your research and those are context and events sensitive. Sometimes, I just won't be able to meet 3 city states, or kill a unit with a slinger, or build an iron mine or found a city on the coast or be able to build a watermill. So, you get better when you understand how to use your location to your advantage in order to trigger those Eureka! moments. That's a very different behavior than in previous versions of this game.