I have both. The combo is a Gries 35 and the head/cab is the gkoelling.
The Gries gives me some of the sweetest BF tones I've heard and the gkoelling takes me to tweed territory. I'm real happy but want a living room amp just because. After that a guest room amp might be nice, or maybe a dining room amp. The kitchen amp is a maybe...not much room and too greasy. If I get a laundry room, or bathroom amp it'll have to be waterproof and that could get expensive.
For me I typically use heads and cabs. I prefer making 2 heavy trips versus 1 really heavy trip Also, on most of the combos I have owned, I have ended up swapping out the original speaker. Where with amp heads, I just put the new head on one of my cabs and go from there.
Combos are great to have around, I have one. Both amp formats have there place.