I would say number 3, without the comma. A comma usually denotes a pause in speaking. Try either sentence out loud. it will help.
You usually use a comma before which if the sentence is broken up into parts.
"He lives in Oxford, which is famous for its university, and finds the rent expensive." is an example.
If you take the commas out and read it aloud it makes little sense, but add a slight pause and it does.
Also if you remove the 'which is famous for its university' out, the sentence still makes sense.
'He lives in Oxford and finds the rent expensive.'
I hope that helps.