There is no right or wrong answer. Different gauges will feel/sound different, and they make strings out of various materials too, so that impacts the sound as well. If he uses the same gauge that Banjo Center has been putting on for him he won't have to make too many adjustments (if any) to the springs and trem, but trying different gauges isn't a bad idea so that he'll know what he prefers. Me personally?.. my favorite strings by far are the Ernie Ball RPS hybrid set, at least for standard tuning. It has been years and I've yet to break an RPS string. For lower tunings I'll use a heavier RPS set.