If its between those 3 bosses,i still prefer meph as he can drop better for me =),tried andy she doesnt drop much nice stuffs for me, but the best place to mf would be in hell act5 the 4 superuniqs(shenk,eldtrich,thresh,pindle),they can drop very nice shit, try mfing thresh in arreat plateau n kill all uniq monster on the way( i found tals,ik n other shit load of items from the champions and uniqs on the way to thresh) pindle aint bad to mf as well,i still suggest a necro or zealot(use stormlash) for this mf runz as thresh has random immune to fire or lite n hammerdins wont do well since frigid and arreats are full of range monsters like quill rats,slingers etc
well i hope this helps u