Personally, while solo, I use Excalibur and do three steps to kill most things that I fight. This is for mobs like RoE 4 and other mobs that you are doing solo. I find 3 steps do a good amount of DMG and is very satisfying.
Maxentius and Naegling when you are are in PT / WS spam content. For me Maxentius is normally the pick here.
So far the Prime is mostly been an idle piece for me, and it has the advantage of having 35 MND on it, which is the highest for that slot. Maybe once we work out better WS sets for it I will find more use.
Other weapons
Murgleis is nice for max magic acc, and of course convert, but I seldom use it for combat
SU5 if you are doing mostly magic dmg. Sanguine Blade can be really nice in certain situations.
Mpu and Mandau I very rarely on RDM
Sequence I never use, and Almace I am to lazy to make.