In
The Gourmet Slow Cooker, Volume II, Regional Comfort-Food Classics, reviewed in another thread, Lynn Alley share some learning from her readers of the first volume.
She used a number of inexpensive cookers in the first go around, and never cooked the same recipe in more than one cooker. Big mistake: some readers couldn't duplicate her successes.
She learned that "different slow cookers cook at different temperatures. One manufacturer's low temperature may not be the same as another's. In general, the low setting should fall between 180F and 200F, and a high setting generally cooks around a hundred degrees higher."
She suggests that you assess your cooking temps by using a kitchen thermometer in the middle of the food, two or three hours into the cooking process.
"So the one caveat I dish out with this book is 'get to know your own slow cooker' and carefully observe how it cooks. Cooking times may vary according to manufacturer, model, and even, I am told, the amount of power coming into your house at any given time or in any given area."
Less expensive models may have hot spots around the edges, while more expensive models make an effort to prevent this from happening. [Not a problem in many recipes, but feel free to stir your food from time to time.] When baking, turn the insert end for end to even halfway through the cooking period.
The size of the pot may make a difference -- a quart and a half size is perfect for single people, four to five quarts work for families, and seven quarts for entertaining. Round are good for soups, beans and grains, but in general the ovals work with the widest range of foods and provide good visibility through the tops.
Regards, Bob