I've got older models of both, I haven't bought any new air rifles in a long time. I have an AA 410TDR modified by Allen Zasadny that shoots ~22fpe, and a FX Cyclone in 22cal. The FX is a little better built rifle, but they are both very nice. Hard to go wrong with either.
The standard AA400/410's are good to go out of the box. The old style had no power adjustment, I believe the new ones do. The 410 TDR was a 12 FPE rifle as delivered. Zasadny increased power to ~22 fpe for ~30 shots. Very efficient little rifle!
I think the AA400/500 series is much better than the FX. I had the comparable FX Royale model and the trigger was poor as compared to an AA. The FX was also very picky about ammo. I currently have a AA 400 and 500 single shot in 22 and 177. I have had a ton of quality airguns, and FX was the most disappointing.
Just got back from the SHOT show. I looked at what was there. The FX had by FAR the best trigger of the lot. It also was the most powerful- up to about 38 ft/lbs in 22 caliber. The Daystate was the fanciest, the AA had a couple of models that I would own. The FX is quite expensive compared to the AA also. I am going to go to Airguns of AZ and shoot what they have before making my decision.