George Ledyard offers a nice commentry on Internal Strength and teachers he has come across
Let me say, first and foremost that I believe that training with any of these teachers will drastically alter ones take on Aikido in a positive way. I would not voluntarily pass up any opportunity to train with one of them if I could help it.
But what you could expect to get from working with each of these teachers is drastically different even though some of the principles of structural training are shared. I'll try to break it down according to my own experience.
The full article and info on the various teachers is here