At CrossFit (every CrossFit gym I've been to, actually) we use the Concept 2 rower. I haven't used anything else with any regularity, but I can tell you they are durable, pretty lightweight to move around, stable, and you can easily stand it up for storage. The display gives some useful info, too (distance, elapsed time, countdown workouts, etc.). I think the Model D is what we use, looks like it lists for $900. Good luck!
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