Else : Best Dx7 import is FM7/8, Rhino will set a standard level for all oscillators (meaning that patches sound like erf ..... nothing after impor ) , and Sytrus is less accurate (but the import function still can be usefull). Didn't test the other import like FM heaven so can't speak for that.
Else : Powerful Fm : Sytrus, and it adds a lot to FM, though the gui makes it a bit hard to program. (Btw the creator of Sytrus expressed his Pov in this thread for those who have not recognised him .....
) Sytrus is really a beast. I've yet to explore this synth to find all it can do.Else : Toxic has some true FM abilities, but lacks some essential features, like individual envelopes, and KB scaling. Though it can make rock solid patches and simple FM, and adds an analog feel of its own.
Rhino is also powerfull (see Himalaya soundset for terrific ambient and cool patches)
Thus for me the FM king is still Fm7 (Maybe because it is very close of Yamaha hw synths, so its a kind of nostalgia ....) I was for sometimes very doubtful in the real opportunity to get FM8, but I wasn't disapointed. It adds even more features.
And afaik no Vsti can import TG77 (or SY77) patches, cos it would imply to have access to the Yamaha copyrighted samples libs of the TG ( The reason why I still have a TG in my rack
)My 0.002 $
LtZ
)
in a rack too, but tbh I use it rather rarely 
