Powerflex for me, from personal experience.
I've not done my current A3 but I have all the bits there to do it, one thing I would suggest is maybe the Whiteline WALK rear wishbone bushes, these alter the caster angle and give you a bit more road contact/grip when cornering.
If you are looking to upgrade the handling they also did/do an Anti-bump steer kit which reduces the bump steer, actually gives you some feedback from the road rather than the soggy vague feeling you get with the standard track rod ends.