Both are obsolete these days. Aerogear is the precursor to Airblade in most aspects. The main difference is that the Airblade series have even more aerodynamic frames than Aerogears. For instance, the AB900 is virtually identical to the AG900, only the frame shape is a little more streamlined. Generally, the AG's seems to hold up longer than the AB's.
I asked a Carlton marketing manager this question and the response was that the racquets were essentially the same, with the primary difference being merely cosmetic. He told me that Simon Archer could not tell an AB 900 apart from a Aerogear 900FX aside from the graphics. However, Mag's comment about the durability of the racquets could very well be correct: not many companies will tell you their new product breaks more easily than their old one.
