Personally reflect would fit better with an entirely different class, rather then any of the current ones[although thats obviously not going to happen]. That being said, the class it 'fits' with most would be scholar. Best fit isn't necessarily all we have to take into effect though.

Scholar got embrava(absolutely amazing) and whm recently got revamped to really be the end-all-be-all of healing and really(and while it could be argued it makes sense for whm to get it; they dont need it). All that taken into account, I think it fits well and would help PLD more then any class at the moment.

It's effects would have to worked around depending on which job gets it as well(if it's only going to be a 1 class spell). As for if it could be subbed; no thanks. We already have so many 'class defining' skills that are now subbed that everything is blending together and losing any sort of distinctiveness. We need more defining(and varied) abilities/spells spread out; rather then just giving everything to everyone at this point.

[Side note: It should most definitely go to Carbuncle as it's been a carbuncle staple for a very long time. It's potency would need to depend on the above mentioned things though.]