I had a Grohmann jack knife with rosewood covers.
They never swelled.
The covers on my Boker Magnum Scout/Camp knife, they've never swelled or warped, either.
From my experience, Rosewood is a stable wood. Also, rosewood has been used on hunting/skinning knives for a lot longer than I've been around. I think its use goes back to at least the 1700's or 1800's.
I only have one knife with (canvas) micarta, a Marbles stockman. I haven't used it when wet, nor cleaned any game or fish with it, but I'd imagine it would be fine. A lot of hunting knives have Mcarta handles these days. If it wasn't grippy while using it to process game, iit probably wouldn't be as popular as it is.
I'd say get the oone you like the looks of best. Both will work.
