Its an interesting question as I think the great strenght of 2000ad is its very variety.
I think this is very much the strength and secret of longevity with Judge Dredd. It's SF, but it's also action adventure, police procedural, dumb humour, dark satire, etc.
Ditto something like Strontium Dog where you get stuff like the death of Wulf and ten year old Moses, the war against the Kreelers, those scary Stix brothers etc, but also the Sternhammer Silencer, "Next prog: Dog-gone!", and the Chums of Dennis.
It's all so different that I'm going to go with Colin and vote
SF as that's the framework that everything hangs off.