After having had one cooking SNAFU after another with our slow cooker (a Crockpot Smartpot, circa 2006), my wife and I are in the market for a replacement.
The main issue is that we are observant Jews, which throws a few wrenches into what might be an ordinary process. It means that we tend to do a lot of overnight cooking (so that food can be ready for lunch on the Sabbath, with the cooking starting the day before), typically soups or stews, and that we can't adjust anything to do with the cooking on the Sabbath. So the basic requirements are:
1) No automatic shutoff for cooking, or at least the automatic shutoff is 20 hours or more.
2) Does not actively detect the temperature (so ones designed to function with a probe are out).
3) Cooks without boiling- the "old" Crock Pots, that tended to cook at temperatures under the boiling point, would have worked fine, but ours will eventually bring anything to a rapid boil when set on low, even when full of liquid. My understanding is that Rival upped the power to deal with liability issues, though I've seen mentions that there may be some available now that don't have this issue?