In my experiance with them, they are on two opposite sides of the spectrum. The Ashdown will get that "creamy bass" kind of sound. I'm not saying it's not capable of getting a clean sound, but it's leaning more towards the pillowy, warm side of things.
The GK, is rather transparent. It has some edge to it, but for the most part, you hear the bass. It would be more suited for modern stuff, slap fiends, and defined tone.
With all that said, I own a GK 1001RB but would like to have, in a perfect world, an Ashdown pre and a GK pre with a power amp set up. Both top notch amps, just very different.
Try them out and see what suits you best, good luck.
EDIT: Looks like Larzito beat me to it. I need to type faster. =)