turbo squid is one I often use...
you can select lower poly... but why .obj?
lower poly object tend to have a higher chance of being 'game optimized' (low poly but also good topology)... but unless you just need objects like rocks and crates, .obj is far to primitive for most game assets.
its a 3D model, but nothing more, depending on what you mean by 'importing' you may have issues. If you want game optimized characters, yes turbo squid will convert characters into .obj but you loose any and all rigging data (some uv's may also be lost) and if you want to import it into a game like a mod, most games need special datatypes, like tabletop simulator (unity) wants you to get the game object ready in unity and then import the 'prefabricated game object' into tabletop, its not just a raw 3D file.