I've heard the RNP on recorded tracks as well as my voice going thru it and its pretty vanilla as far as pre's go.
That being said the MS1b is what I settled on A for price point and B it sounds slightly more authentic as a vanilla pre.
Plus Roger Nichols says this pre amp rocks and that he pulls it out from time to time to record. The MS1B sounds fine on vox and bass, but its no DI and you need a good DI (Radial) if you're going to record bass DI to a pre. This preamp has that immediate fast sound too it in my opinion. Its good for singing, rock, blues and pop/hip hop requirements. Its got enough gain to drive something like an SM7
It also uses Burr Brown chips which explain its nice sound.
We used the MS1b for all of our vocals on the myspace, but I hate the mixes they're all over a year old! The new ones sound better.