Hey poptart!
I've found the Portabass to be a springy, lightweight, little gem in the Ampeg family. The 250 has some seriously solid punch, and on one of the combo models I believe the head is removeable so that you can use it as a combo or to drive an 8 ohm cabinet. It's a pretty solid buy. If you're looking for something more like what you're probably running right now, the SVT Classic remake is absolutely stellar in my opinion for crisp clear tube tone through and through. I'm just not sure if you need to be lugging around an 80lb head and cabinet or if a combo will do. Do you really need the tube tone?
That's your call. Let me know more if I can help!
Peace,
ShackMan