I believe that rubber is better, as it will not absorb scent the way that leather will. That said, I'm not really sure that it matters either way if you practice dedicated scent control. I wear rubberboots through bow and blackpowder season, and from a month prior to the season on the boots don't even come indoors. For later in the season I use all leather Danners, partly because they're warmer than my uninsulated rubber boots, and also because I don't think the scent is as much of an issue when it's cold out (scent doesn't disperse as much).