If you want the best bass combo then you're going to have to buy a Trace V-type.
Not your average ladies lightweight, I'll have half a shandy combos there, just pure grunt and one of the best sounds I have ever had, certainly the best of any combo I've used:
1) Twin valve preamp - none of your pretend one valve warmth nonsense or Ashdown grind knob - this will overdrive to buggery
2) Its a Trace Elliot so its louder than it says it is and reliable as they come
3) It has one of the simplest but easiest to get a fantastic sound preamps I've ever used
4) Linking a 1518 cab to it will have the back of your trousers flapping
5) Its manly
)0 it has a line in for your iPod
There are others who will back me up on this but this is, of course, my own personal opinion on combos.