My SIL bought us a Rival crock that was wonderful for our wedding 16 years ago. Still have it, but it's HUGE and there is only the two of us. Plus I thought I would like a black one to go with the rest of the appliances.
I started with the decorative black and stainless Rival - burns everything.
Next was my Kitchen Aid, it has a rubber seal around the glass top and the temps were just right - unfortunately the crock cracked. Kitchen Aid replaced the crock, however the replacement crocks aren't the right size and now the lid doesn't fit right. Dam expensive experiment.
I bought the Hamilton beach seal and go with a padded rubber seal on it (yes, I do like the seal - else why buy one of the silly things? the moisture retention and low heat are what makes the meat oh so tender). It's white, but it works.
So what do I use the most? The big ugly Rival that I started out with

I read somewhere that the lows were adjusted up to prevent food poisoning. Who knew that the crock I had for the last 15 years was bad for me
I'm not buying any more until they figure out the crock liner issue. I am SO careful with the liners, always hand wash, never put them in water when they are still hot, yada yada.
Good luck!