grammar nazis. i.e. "most" means Very, it's a superlative and more often than not points to one object instead of many. Furthermore, the wording of the title chose "monster" as opposed to "monsters" meaning that there should be only one....
all jokes aside though, bow guardians are easy with pneuma. What is most annoying in Thors are the sword guardians with their spear boom of death... Sure we can pneuma them too, but BGs don't kill you in one hit, SGs do...
Hodre and hell poodles and flame skulls shouldn't be a problem as rachel is neutral (thus dark attribute does not mean you have to change your weapons that badly) and nameless parties usually consist of SG spamming wiz or snipers with holy arrows or sinX with holy katar (again meaning that you don't have to change weapons)...
furthermore, hodre's card is actually very good, hell poodle's card can be useful if used effectively, and flame skulls are so easy to kill they shouldn't bother anyone...
ridewords are also annoying, but their drops are decent...
mimics and hunter flies, on the other hand, spawns in places where newbies can train nicely were it not for the existence of those monsters (muka, EDs, marduk)...
so my choice would be: Hunter flies, they spawn in more "newbie" places and more annoying than mimic as a whole (especially since mimic's card is way better than hunter fly's)...
-w-