I like both but I think from now on I'll be getting combos. I just switched my Mark V from a head and closed back cab to a combo and don't really miss the added tightness and low end from the closed back cab while I really like the "change" (hard to describe) that happened with the med gain to clean tones upon moving to the combo.
I HATE closed back cabs - too directional. I played all last year in a stoner metal band with an open back cab. No issues and the tone filled out the mix a lot better.
My preference is one great 2x12 cab and a couple of heads for various uses. You get that airy open back combo sound but only need to own one cab and heads are cheaper than combos and easier to work on if needed.