Addressing the end first: I’ve not used CGC. Do they use different holder materials than CSG?
I don’t know how I feel about your comment on BVG and CSG. In my experience, SGC tends to over grade vintage, which would make them closer to BVG.
SGC built their reputation for grading vintage during their “green label” ownership period, when they were owned and run by CCG (the current company that controls CSG & CGC). The new SGC (black label), which has no connection to the original SGC (other than name), uses non-sequential holder numbering (which makes it easier for graders to sell their own SGC submitted cards), was operated by an widely alleged card doctor, and has no policy against its employees and graders submitting and dealing in cards graded by SGC, relies on the hobby’s elevation of grading status.
CSG has hobby veterans on its grading team and backs their work with a grade guarantee. SGC and BGS have no such policies. PSA has a policy in place that is similar to CSG’s.
CSG does have a policy in place to charge for cards that exceed a certain thickness threshold, but that is because they use special thick holders for those cards. I’m not even sure SGC would grade those thicker cards, period.