The starter is bolted to the engine as close to the engine block/starter is the best place. Grounding to the frame of the car you have to go through a ground cable/strap to the engine which is a potential point of bad connection. You usually have a large ground strap from the engine to the body and then a large negative battery cable from the battery to the engine block. So connecting to the frame your going through whatever bonds the frame to the body then the strap from the engine to the body.
\My very first truck was 1988 chevy which we got from a repo auction and someon had improperly installed a body lift. We found that the large negative battery cable was left disconnected since it wouldn't reach and it then melted the small negative battery cable. When we foudn this we took the body lift back off and reconnected the large egative battery cable but didn;t think to check the connection. Since it had been disconnected for sometime the connection point had been exposed and started to rust, then reconnecting it on top that rust didn't help any. I couldn't get it to crank one day and wiggled the battery cable and it started, then disconnected the cable from the block and found all the rust trapped under it and cleaned it up good and it was fine for many years to come.