I disagree w/ ya this time Lobi. It's my belief that for any Mandau addicted enough to XI (more than myself atm apparently, since I have none of the following), you won't be all that you can be without having all of Fire & Thunder Kila, OAT Para, & Auric in your arsenal. Ignoring Twashtar of course. My belief is that if one were to create a 3-dimensional(+) model with an axis for pDif, hit rate, a ratio of avg engage VS disengage time, (etc), the answer to the optimal dagger would depend on what your current status was with respect to these values. S(hit)i(s)S(ituational) right.
Same thing for non-Mandau thief. The recent daggers are quite epic. Having multiple weapons in your arsenal, whether have a Mandau or not, is nothing new. Blau, X's, Ridill, for example. Well I guess that's 3 choices for the Mandau user of olde and only 2 for the normal user. I think SE is just doing a better job at releasing good situational sh*t with these magian trials.
I'll also attest again to my opposing view to the old "you have to be less concerned about TP gain after you have Mandau." Reflecting upon my many chronicalingz, it seems that sh*t was not always so simple. Long disengage times, feather tickle, people & mobs moving, refusing to be TA'ed, hate being glued to you, dark ixion, slimes, meleeing something in einherjar along with 20 other people; the list goes on. In my experiences, better TP gain has usually been a good thing. I'd contend that the value of TP gain is highly underrated among Mandau users.