The natural way that most people speak is to put prepositions at the end and to use who as both subject and object.
If you're someone who speaks in a register which means you don't leave prepositions at the end of a sentence, there's a very good chance that you'll also be someone who will follow those prepositions with whom.
It's quite rare to find someone who moves their prepositions from the end but who doesn't use whom after them, though you may hear it on occasion, especially from people who are trying to raise their style.
I'm thinking of something like a university student giving a presentation. In an attempt to make their speech sound more intellectual, they may try to emulate other highbrow speech attempts by removing their prepositions from the end, but not be sufficiently well versed to place whom after them. It's certainly something that I've seen happen before on a few occasions.