Geez....I had four slow cookers and actually gave one away (....it was an old one from my mother that didn't have a removable crock pot). Do get one with a removable crock as Jacque suggested (it really is very important as far as cleaning ease).
As for my other recommendations, do choose one with a timer that will put your crockpot into warm mode after it's finished cooking. It's one of the best feature ever developed. I sometimes work a 10 or 12 hour a day and I love coming home to food that is not overcooked. I time my food to cook on low for 6 hours and send it into "Keep warm mode."
As for what I do own...I have a large Rival (gosh, it must be 20 years old) which doesn't have the timer feature but does have a removable crock. It cooks wonderfully but I simply can't let it cook all day and it doesn't have a warm mode (just low and high).
I also have a Versaware Pro....it's supposed to be fancy...you can saute in it, put it in the fridge etc...but it's really not all that. Because of it's shape (my belief), my food tends to dry more quickly. It never stays as wonderfully moist as the food in my old upright Rival Crockpot. What it does have (over the old guy) is a fantastic timer feature that allows me to slow cook for a certain amount of hours then it then shifts to a warming mode. Because of that feature, I use that crockpot the most. I don't want burnt food. I also have a small Rival, I used to use for steel cut oats...but I bought a Zo Rice cooker so I never use it now. It was great back then. Anyway.....
When I do buy another crockpot (probably next winter)....it will be upright and have the timer feature. I haven't bothered yet because the Versaware Pro is doing okay. Only okay. I still wouldn't recommend it only because I it tends to be more drying then any other crockpot I've ever owned.
My recommendations: Buy a removable crock that is narrow and upright (keeping the moisture in the food), but make sure it can cook on low, high and have a warming function. The timer is especially important if you are a working person. Ignore those expensive ones that promise saute and refrigerate functions....you really won't use them, but don't discount the timer function...it will come in handy.
(Please note there are also 2 Versaware products.....the less expensive one doesn't have the timer function. Don't be fooled. I honestly don't recommend either one.)