My use would be to clear/improve about 12 acres of woodland on the farm. There are several down trees and lots of brush that needs to come out.
Any need to clear a path as you go?
While I completely agree with the statements about a narrow grapple being less likely to get in the way while in the woods, I personally went with a 66" single lid (item# ETA-SLRG-66) for my
L3560 as there is potential I'd be using it to clean up storm/tornado damage, and figured wider was better since it'd improve the odds of keeping things out from under the tires (especially things that could potentially damage/puncture the tires). Granted that doesn't cover the whole width of the tractor tires (running R4 tires on mine), but it does get just about everything that isn't capable of sliding between the tines.
So if there's a need to be able to clear a path, or use it as an impromptu landscape rake for pushing brush/limbs into larger piles I wouldn't rule out a wider grapple (if it won't get in the way). It can be really handy to run an just above ground level to push limbs/brush into something worth stopping to pick up - especially if you're having to do much driving between where you're working and where the material is being put.
However, if you're planning to do much ground engagement with it to remove brush/roots I think narrower may also be better as you may occasionally find yourself being traction limited depending on how much, how big, or just what you're pushing against. Not exactly enjoyable or productive to find yourself with all four wheels spinning and not making forward progress.