well personally i would think GS (as a ranged char) should do pretty well in items trial (bullet/rapid shower spam FTW)...
and monster trials should be doable too with the proper rapid shower / full buster switch.
and SGs supposedly own PVM, so i think the only thing you need to remember is to spam fish while kicking at 190 Aspd, and don't forget to bring the proper gear and to set up the proper stances and winds...
so in the end i think it's about your own preference. I would personally choose a ranged character if my connection was good. But SGs have running (VERY useful in monster trial, especially if you see the pros failing at the round you're about to do xP), break fall, and could easily stun lock and decimate monsters if you take care of them properly. SGs should easily pawn the 10-7-5 mobs with his AOE kicks and take the larger monsters on one at a time to ensure victory.
-w-