I find that 2x12's sound tighter and have a bit of added compression - I like this, you may not. They also have less bass, but it's easily eq'd around.
I want a Marshall 2x12 oneday.... i saw a nice used 80's JCM 800 era 2x12 but the guy would not sell it without the head.... The only reason i want a 2x12 is a 4x12 will no longer sit in my new car.... a 05 Camry.... right now i use a Marshall 1x12 but a 2x12 may come in handy...... for sound reasons i'd love the 4x12
i'd get the 2x12. i had the marshall 1936 2x12 and it was great. it sounded just like a 4x12 but was very portable. the extra 2 speakers are not worth the backbreaking transport issues.
I use a 2 x 12 cab with my Marshall DSL50, and it sounds very punchy and very loud when cranked....but tight. I'm using Vintage 30's for speakers, and they sound pretty nice.