I don't use a testimonial-specific plugin.
Generally, I would just create a "Testimonials" category and enter each testimonial as a separate article/post in that category.
Users could submit testimonials through a standard Jetpack contact form.
Then the Admin would copy the content to a new Testimonials post.
It seems like maybe you're looking for the testimonials to be automatically published, without work or review by an Admin. Obviously, the manual solution wouldn't work for that.
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You might find that presenting the testimonials in a way that users can easily sort might require a separate solution.
Again, if I was doing it manually and needed sorting, I would use a plugin like YooTheme's Widgetkit (scroll down to look at the "Dynamic Grid" examples).
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demo.yootheme.com]
You would define the Testimonials category as the content source for the Widgetkit grid, and then use Tags for sorting.
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This is how I've approached testimonials in the past, but I know it might not work for you if you need to deal with lots of testimonials with limited Admin intervention.