Interesting.
Do they both list your "change" addresses?
I ran both, compared the output, and found that "listreceivedbyaddress 0 true" listed 7631 addresses, while "listaddressgroupings" listed only 5283. The 5283 was a strict subset of the 7631. The missing 1.5k or so addresses apparently never received any coins.
If you're hunting for CLAM, it's a waste of time to search in addresses which never received any CLAM, so the shorter list, from "listaddressgroupings" is probably the way to go.