I'd like to but that would take a couple of pages to do it any justice, but here's a readers digest version:
From my point of view it's a question of the "quality of detail" more than anything, by which I mean how well each detail part is rendered.
The drive and ideler are too flat and details poorly proportioned, the tracks are better in the DML kits, though some might like the rubber band tracks better, the clear hull and turret can't really be seen through, but if you paint it it's missing weld beads and texture, the engine deck details (screens, etc., especially the side screens) are fairly poor (though I like the fact that the made some attempt to represent it "true to form"), the list goes on and on.
And, for me at least, the fighting compartment interior leaves something to be desired, fixable but annoying.
The engine/transmission compartment and turret details are pretty nice, though.
The AFVC kit biggest advantages are its lower hull and suspension, less the drives and idlers, and it's comparatively low retail price.
The DML kits, though nothing like "perfect, are overall better rendered.
Mark