Generally you get what you pay for, I have a 4-jeri on one bike that I use as it lets me run 2 gears. It keeps ok tension, is pretty sturdy, but not hard to hit and it does tend to bend the mech hanger. On my other bike I have a 74kingz which keeps immense tension and is really out of the way. I also hear Rohloff are great, and if you have a sub 13/14 rear sprocket it would be better to get a two jockey wheel system as it gives better chain wrap with smaller sprockets. I have never owned an un-sprung tensioner, but I have heard that they can slip and loose tension so I would go for sprung. In short, buy a 74kingz if you can afford it. If not, and you tend not to hit the mech/mech hanger go for a sprung tensioner with jockey wheel.