Well shoot, I'll bite.
In order of decreasing frequency to the best of my knowledge:
Cavalier (by an order of magnitude the most common)
Infiltrator Mk. II
Grenadier
Hauberk (probably very close to similar numbers with Grenadier?)
Infiltrator Mk I. Sloth (Huntsman, Interdictor, etc)
Fusilier
PAB-28
Sea Fox
I'm sure there are some Grey Death and IS Standard suits in the AFFS, but I believe the above list forms the bulk of the AFFS BA forces. Lastly, I remember reading Clan Medium "Rabid" suits were also in use, but I would guess they would be very infrequent.
Cheers,
Mad
Edit: Confused Waddle with Sloth, woops!