Does no one own a crock pot? Not a single DR, except for our DR MBarnum via telephone, had any consumer thoughts.
The number of quarts depend on a number of factors:
Is it just for you?
Would you be using it to prepare foods for pot lucks or feeding up to 12 people?
Most crockpots are very reliable. The more controls you have, the better for you. You need at least a "High" and a "Low", but you're better off getting something that lets you set how long you want something to cook. You'll determine this from the booklet that comes with each crockpot, telling you recommendations on how to prepare various foods.
I never use this item with frozen foods...I always use fresh, or in the case of beans, dried.
Rival, Hamilton Beach, Sunbeam and Cuisinart all have fine models in different capacities.
My first was a Rival. It was a small pot and I could have used one larger. I bought one, eventually, by Sunbeam. Both have been troopers for me over the years. My Rival is currently 35 years old (my mom sent it to me in 1973 when I was stationed in Vicenza, Italy), and my sunbeam is 33 years old (I bought in the Naples, Italy, Navy Exchange in 1975). Year before last, I bought a 6-quart Cuisinart for my pot luck events. I also make my Brunswick stews, BBQs and soups in it. I put the food in containers out of the crockpot and into the freezer.
My Rival is about 2 quarts. My Sunbeam is roughly a 4-quart model.
If you think you'd want to prepare only a meal's worth of food, get a small one -- 2 to 2 1/2 quarts. If you don't mind leftovers or would like to freeze some, get a 4-quart model.