I researched several. I was concerned about comments individuals made about blurry lines while looking through a tube. Many have bought cheaper refractometers on Amazon and have been happy with them. I'm not sure about their accuracy or quality.
I believe in buying the best quality your finances can handle. In the long run, I have found it the cheapest route. Regarding your question, my choice was Milwaukee MA871 Digital Refractometer and I have been very happy with it.
I believe in buying the cheapest one you can, and without any SG readings on the right side because they are notoriously wrong. Only a conversion calculator like the one at BrewersFriend.com can accurately determine the conversion from Brix to SG.