Iv been playing MNK since Beta, beat T1 to T9 on it and all primals acessble, switched to NIN after patch and 4 days after i went to do some T6-9 to practice, then i beat T10-11 on NIN, it took some practice but now i feel fairly at ease with NIN so i finally can compare bouth.

MNK only issue is knowing fight good enough to know how to keep your stacks on, and ofcorst posicional attacks but luckily he wont drop its combo when hitting wrong side.

On NIN on the other side u have to deal with two separate cooldown timers (mudra + buffs/dots) constantly muving against each other (combat disengages, mudra lag) so i have to say, at least for me NIN is much more heavy managment than MNK and i have to try REALLY hard and dont miss single mudra to have comparable DPS to my MNK wich is now 4 ilvls lower.

I also did T10-11 on MNK and it felt much easier to get to DPS that im happy with.