Advice on ebay 4 stroke kit.

Hi guys! New to the community. Recently built my first bike. 2 stroke silver slant from bike engines. I love it. Looking now to build a 4 stroke. I'm looking to get a cheap kit on ebay. Question is, I see 2 different kits for the same price. One has a small silver metal transmission cover (I assume chain drive?) And the other has a large black plastic cover (I assume belt?) Which is better in y'alls experience. Just looking to have a fun project and build. Cheers!