That all depends on whether you want Asus apps and features, or the latest version of Android with a little more customization. Personally, the fastest stock rom I have used is CROMi-X, which can be found in the development forum. v5 was recently released, which is based on the latest source from Asus. Definitely good to try that rom out if you are a first timer, there is plenty of support and you will find the speed boost to be really nice.
Then there's Cyanogenmod 10.2, which is quite stable on the TF300 now and it is what I am personally using. It doesn't include any stock Asus apps at all, it is based off the official CM sources. To be honest, the performance with CM10.2 is really quite good and there may be some kernels coming that will allow us to even overclock :good: