I think I prefer the Laney, looks-wise, to the Martamp's Marshall styling. Lord knows how they compare soundwise though.
They're all very different. All have their thing really the Jet City does the high gain stuff, the Goldstar the low vol stuff with a nice rock crunch and is mainly used for testing pedals. The Laney really has it's own thing going on. Meaty and very even sounding across the frequency range.
My D6 does cleans VERY well, better than all the above. It's not as happy as a crunch machine, the Goldstar does that side of things better. The good news with the D6 is that it loves pedals and you can get all the crunch you want from them.