Having flown all the types of aircraft at Eagle except the CRJ, I will say that the Saab is the most challenging to master. Systems on it are a mess. But do not be intimidated. Anyone can learn it with the right aptitude and attitude. Eagle's training is good, and thorough.

If you can learn the Saab, you can learn any aircraft. But I've heard of people failing ERJ training too. So just pick the aircraft that you want.