Both are great but different sonic flavors. MBL will be more liquid in the mids, but Krell will be "precise" sounding. I would add Spectral to your list if you have the upgrade bug. The only thing are the cables. Spectral is special. For the money new, they will really give the others a run and you might prefer them.
If I was making the choice, I would have a very difficult time deciding. There is no BEST, but what do you want.
If I was making the choice, I would have a very difficult time deciding. There is no BEST, but what do you want.