Mutsu isn't faster, it goes 39 knt max (not sure about hyuga but iirc it was something like 39 or 40)
Both can use same guns (dual 16" L, type 3 or 90, ur choice)
Both have 7 support slots
Hyuga requieres higher BO lvl, has more life and 6 guns, while mutsu has only 4 main guns but better FCS (what means better spread)
I'll get the hyuga, great range, great firepower, and higher lvl (for lvling purposes), and since it's an "old" EBB, cheaper than mutsu (same like KM O-Pro-II, a great ship, boosted and considered 'old ebb')