Rick is right, the Q stands for the plugit, which is why the atf 55eq doesn't exist. Link to thread with abbreviations
As for the mtf3, both types will work.
We have both models, but I prefer using the atf with the old style rails. The steel baseplate tends to make scratches in the green slide tape, and those scratches increase the wear on the alloy base of the ts55.
But if you have just one saw, this shouldn't matter.