I just ordered an dreamcast on eBay and eventually want to get CRT monitor to try out the VGA as well as I have an OSSC which has VGA inputs.
Was originally thinking of getting the official VGA box until I saw the compassion video of the crushing black.
I believe the ones made by Behar Bros are usually the recommended ones. They have a few different models, each with different features (like a couple have a scanline generator built-in and/or SCART output), so it’s up to you to decide exactly what works best for your setup.
Just as a disclaimer, I don’t actually have any of their products, but it’s definitely what I would buy if I weren’t being cheap and just using the low quality cable that I already have.