I use Radial J48s for the bass and guitar in my acoustic trio. I'd say you can't go wrong with the J48, JDI, or Countryman Type 85. I really don't think there's any need to drop $500+ on a U5 or REDDI, although they are superb. If you want some tone control, I'd recommend the SansAmp ParaDriver DI over the Bass Driver DI because the PDDI has a semi-parametric mid control that comes in mighty handy.
Agreed - I like my Countryman, but don't mind using any of the above... I also prefer the Para for it's mid controls...
- georgestrings