I normally don't think of close assault units as skirmishers, but if I had to use one of those two badly suited alternatives in that role, I'd probably go with the GHR because of the LRMs-5 rack, so it's not as heavily forced into knife-fight range to be useful.
To me, "heavy skirmisher" is practically a contradiction in terms. A skirmisher is supposed to avoid melee combat and rely on mobility and ranged weaponry, where a GHR or GLT is primarily designed for brawling, and a Charger is practically incapable of skirmishing with its 5 Small Lasers.
I'd consider an Ostsol, Quickdraw, or Dragon to be about the closest you can get to a "heavy skirmisher" in the 3025 era. Anything slower can't avoid melee combat with most standard "line" units (at 4/6 speed), and is therefore not a skirmisher.
[ It's like asking which is your favorite racing tractor. ]