ok, as the resident curmudgeon, i'll jump in first:
rotosound rounds on the fretted basses - 5 string MK deluxe. never had a problem with a weak B string, i like an agressive, in-your-face tone out of this bass that says "yeah, i'm pretty and i got tone for days, homie. now what?"
thomastic flats on the fretless 5-string essence - as far as i'm concerned, a fretless bass's raison d'etre is that stand-up acoustic bass growl, other may not agree. no problem with a wimpy B string here - i've been using these strings for years on my fretless basses and never been let down. They seem to have lower tension than other strings, which may or may not work for you. I think this lower tension contributes to the temperamental issues i have with this bass, the neck likes to go wonky on me when the seasons change (as they are now).
hope that helps.