My 2 cents:

1- I don't think that T4 (T3-T2) styles are bad; to the contrary I think that they are the best. The issue with Yamaha styles are no the styles by themselves; If you put the drums of the Audya on those they will be even better.
I think that the Audya styles need more orchestral sounds. Some times they are drums/bass dominated.

2- I found the Audya easier to use than the T4.

3- For giging, no question that the Audya is more adequate because the Audio Drums. They produce a more lively play.

4- For home use and for musicians over 50, no question that the T4 is a bigger atraction. For that reason it dominated that segment of the market. Older audience are usually more sensitive to "loud" music. Add to that OS stability and customer support.

5- Right hand sounds (SA sounds) on the T4 are excellent, better that the ones that we found in the Audya.

6- A big advantage of the T4 is big amount of styles available (factory and 3rd parties). There are a lot more after market tools available for the T4 that for any other arranger, to create styles.

7- If I will purchase a Yamaha keyboard, it will be the PSR-S910 and no the T4. More value for the money and almost same features.