They all will work just as well.
The ABF is a tall block, which means literally that its a bit taller

Audi blocks are short blocks as is the 9a fitted to the Passat & Corrado I believe.
With an ABF you may have a problem with the throttle body touching the bonnet, but a few taps with a hammer sorts this out. You also may get contact between the zaust & tunnel, again a few bashes with a hammer will sort this.
The other option is to modify the front engine mounting to tilt the engine back a little, or get a spacer for the zaust manifold -> downpipe.
With the short blocks its a case of bolt on and forget, but if you go for an Audi lump you have to swap all the anxileries over from your old 1.8 lump.