I surveyed 22 different testimonials plugins tonight (!). This one wins "best in show".
Gorgeous default display. I love the way it has a space for location (good in testimonials!).
Does a great rotation in Ajax.
Tons of options in widget.
Just turn off rotation, and it does static instead.
Also can show testimonials on a full page. Could use some CSS formatting, but otherwise good.
In order to make more than 1 testimonial show up at a time, you have to use multiple widgets, and specifically decide which row you'd want any particular testimonial to end up on. It would probably be an improvement to be able to show more than 1 at once, but this is not a huge thing.
Built on custom post type, so does import/export.
A tremendous amount of options, but great defaults.