My only input is; I have one that sits on the base/heating element and if I had to get one again, it would be the same style... if they still make them. I like being able to take the food right over to the table in the pot and set it down on a towel. When it cools off I will put plastic wrap over the pot, put the lid back on to make a seal, and stick it in the fridge. Then it can come from the fridge right back onto the heating plate when you are ready for leftovers. I find this style of slow cooker pretty handy. It is the low oblong style.
BTW... they make electric pressure cookers now that can double as slow cookers. They come with a different lid.... just a thought