Hello, that's kinda like asking what kind of car to buy.
There's a lot of options out there and from what I've read, many of them are very good products. I bought the C11 because it looked to me like it had the most functions that I needed for my project for the lowest price. It's now working well but I had a VERY hard time getting the speed control working due to my lack of electronics knowledge and total ignorance of the isolation issue with my KB SCR speed control. I had to buy a separate KBSI-240D signal isolator to get the speed control to work.
Some portions of the manual were unintelligible (to me) The seller, Arturo Duncan was quick to respond to my questions but I just couldn't understand what he was trying to tell me and I got very frustrated. I think the prioduct is fine but the manuals need a total re-write in some areas for cuttomers like me that are weak in electronics . Will I buy another one if the need arises? Probably so if I'm still on a budget.
Another ORAC owner/retrofitter I've corresponded with uses a Campbell Designs B.O.B and he's very happy with it. It has onboard power supplies and I think it handles the SCR speed control isolation problem differently. It is almost twice the price though.
I wouldn’t go with one of the many cheap units you see on ebay and would recommend staying with an established product that has good support. You can find a lot of info here and on other sites online that my help with your decision.
Good luck and post lots of pics of your project!