Definitely a personal preference thing. I pack really light and have been touring on 25mm tires lately. That said I did a mixed dirt/pavement tour on fat mtb tires with lots of low knobs and was surprised how well they worked out even on the pavement. I plan to continue to use skinny tires on the pavement.

I will add that the tire construction probably has as much effect on ride quality as width if not more. So the width of 2.1" Kenda Slant Sixes that I used on my pavement/dirt tour was actually less of a detriment than the stiff sidewalls of Marathon Pluses in 32mm width. The MPs are the worst riding tire I have ever tried. I took them off and sold them after a couple hundred miles. Additionally the 700 x 32mm MPs (810 grams) were heavier than a 29 x 2.0" Kenda Slant Six (730 grams).