I'm a /nin type of meleein rdm currently with Blau/Joy.
I'm at the point of deciding between building towards a Badelaire +2 or a Khanda 2-4.
Would either be a poor choice? Or what sort of circumstances would make one a better choice over the other?
Ignore Rog, he is a moran.
Blau/Joy is fine it is going to be your highest damage output source in Abyssea before getting CDC. CDC is a game breaker because it is a Crit WS that RDM can get naturally without having to sacrifice the sexy that is an off hand MA weapon, while keeping a decent damage MH.
Badelaire should be your first sword upgrade. The Joyeuse is still a very strong weapon as far as DPS application and TP gain rates are concerned. (it is .5% less potent than the khanda 2-3*, and likely 2-3% behind the 2-4*.) Once you have CDC you are laughing and can either choose to get the Khanda 2-4 (please see the note) or not worry about it the difference in the end will be barely noticed however.
Another option in the mean time is to work to getting the Dagger that has the 40D Latent: Mercy Stroke, or the new Twilight Dagger (i think) which is also 40D. Which is a nice increase to a 5hit crit WS like evis. But currently in Abyssea CDC is king.
* Note the ToTM MA weapons 2-3, and 2-4 only come out ahead of the joyeuse when WS damage is factored in at a 100% constant rate, this means if you hold TP at the tail end of a mob, or because you are aiming for certain !! they both begin to lose ground to the joyeuse. This is due to the sexy low delay (224 vs 262) during the TP phase.
In regards to Rogs second half statement, you will likely out damage your melee via nuking, but since this wasn't your question It is kind of a redundant point. This is due to the scaling of T4 spells vs the scaling of melee damage. However the largest factor in the argument is the bottomless MP factor and the need to never need to rest. However in situations (which are usually rare for a RDM melee because it is still frowned on for some reason, yet DRK's and SAM's still get party sots) where you have 2x March a good melee set with RR atma at the least will give a nuking RDM a run for its money.