Some pointers in choosing AAH/AFC heads for building...

One of the best things about having an extra set of heads around is the ability to take plenty of time in re-building them and not find yourself in the position of needing head-work with the associated down-time of your daily driver.

Also many of the facets of head work can be accomplished in stages at a head shop and don't have to all be done in one fell swoop. You can have them clean and disassemble your heads initially. Then pick them up take em home and start the porting/polishing/gasket-matching tasks along with smoothing the area on top of the head (under the valve cover) so that oil doesn't have so much rough surface to cling to and can drain back into the oilpan quicker. There's MUCH room for improvement in that area alone on these heads.

Later, as time & funds become available you can return to the head shop to have them install new valve guides and/or valve seats if you plan on going with larger valves. Then return home and back to porting/polishing around those newly installed pieces.

Back to the head shop a final time once you have your valves, lifters and springs in-hand to let them install the new valves, seals, springs, retainers, keepers then lap the valves and get everything to the correct installed heights and fly-cut the head mating surface flat and square.

Now you start aquiring all the bits and pieces necessary to do the installation. You should do Audi exhaust studs, nuts and washers. DO NOT use just any stud, nut and washer that will work. Audi exhaust studs/nuts and washers are the best you can do bar none! You'll also need all new cam seals, head gaskets, IM gaskets and valve cover gaskets. Wouldn't be a bad idea to consider an EGR clean-up/replacement while in there as well as a new valley pan gasket. There won't be any easier time to do these things.

As far as head selection here's some good/bad things about each head:

I would personally still choose AAH heads today to rebuild rather than AFC even tho the AFC in stock form would outflow the AAH heads. But in "rebuiding heads" to "stock" specifications today I'd opt for the AFC heads on an AAH or AFC engine with AAH cams. Basically if yoiu're going for 270-300+ HP the AAH heads would be easier/cheaper to accomplish it. For ANY HP number lower than that the AFC heads are the way to go and for the very same reasons.

AAH uses a dual valve spring while AFC uses a single spring. The AAH has hardened spring seats sitting below the springs that allow using even heavier springs which allows higher RPMs (if stand-alone is used)while preventing valve float. The AFC heads would require machining and hardened seats made to accomplish that. Any valve stem diameter can be installed in either head with appropriate valve guides. And a total of 2mm larger valves can be used, ie; 1mm larger int and exh or 2mm larger intake or 2mm larger exhaust. It is possible to use 1mm larger each and retain stock valve seats tho larger seats will always flow better.