Length gives you stabilization, meaning enhancing the ability to hold steady. I've not gotten much stabilizing effect from anything less than 10" and I consider anything shorter than that to just be a shock absorber and counterweight. So if you want something for tournament shooting, you want a long one. I'd guess you're going to be shooting one of the bowhunter classes so that puts you looking for something 12" or less in length.
I always shot either Compound Unaided, Bowhunter Fingers or Bowhunter Release classso my stabilizer had to be 12" max. I also had the 12" max rule for the NFAA classes I shot. So, I used an old Doinker Shorty mounted on an aluminum extension rod I made up to give me 11.5" total length. The combination of length and having most of it's weight on the far end combines to give me more stabilizing effect than either one alone would give.
Originally I just had a piece of brass on the end of that extension, but replaced it with the Doinker when they hit the market. When I go hunting, I just remove the extension and use the Doinker by itself.
You can't have mine.

But it'll give you an idea of what I'd recommend you look for.