It depends on the type of semi.
On rangers, armsmaster, and combat-oriented type, I would say the two handed sword.
Or, for maximum shield/weapon combination, the falchion. But that's, actually, the best choice for EVERY character, powerplaying-wise.
Obviously, in a CC/MAC POW and with options, and/or flavor-wise, then any weapon could be good for a specific character.
I especially like the shield/mace or shield/hammer combination, beacuse they both fall in the same category (RMSS/FRP) and if using weapon similarity rules from RM2 (don't know if something similar catually exist in RMC).