Well, Ambidexterity und Two Weapon Fighting in AU do not work like the 3.0 (or the 3.5) counterparts, the AU version is better, since if you have both feats, you suffer no penalties when using a light weapon as an offhand weapon.
If you only have Two Weapon Fighting, you are approximately as good as a 3.5 character having only the Two Weapon Fighting feat. (One Attack at no penalty, and one at -4 if the offhand weapon is light compared to -2 to all attacks and one extra attack)
Its probably a matter of personal preference what you choose.
One feat makes it easier to become a two weapon fighter, but you are never as good as with both feats. (Unless you decide to mix AU und 3.5 rules, so you only need one feat but gain the benefits of both AU Feats - which I would consider unbalanced).
I always liked the concept of having an Ambidexterity feat, and I like it even more with it being a talent. But I always thougt two-weapon fighting was inferior than one-haned weapon fighting with shield, especially since you need two feats to get the two weapon fighting route working at all. I would use the AU system, it adresses the problem and keeps the flavor.
Mustrum Ridcully