I have a Proctor Silex SB from Wally World and a Cuisinart from Amazon. Both have a detachable stainless steel head, and I agree with the others that these features -- detachable and stainless steel -- are absolutely non negotiable. You can put a detachable head through the dishwasher. You can detach the head and leave it standing in your batter if you want. The stainless steel is lye and heat resistant.
The PS was the first one I got, and I liked it pretty well. If you have a limited budget, it is a good machine for the right price. The bell on the mix head is like a bowl shape with no scallops or perforations, so the bell tends to vacuum itself down to the bottom of the container if I put the bell straight down while mixing. This SB really needs to be at a slight angle from vertical to work right.
About a year ago, I treated myself to a Cuisinart. The scalloped base of the Cuisinart prevents the bowl from vacuuming itself to the container and the scallops let the soap batter (or lotion) mix better regardless of the position of the SB. This one can sometimes feel a little too powerful, but I've learned to just "bump" it on and off if I need to reduce the intensity of the mixing.
I now reach for the Cuisinart pretty much all the time. I occasionally use the PS if I have a very small amount of lotion to stick blend -- the lower mixing intensity of the PS can be a real advantage for small batches. If I had to pick just one, however, I'd go with the Cuisinart.
I also have a fancy Bamix stick blender. After using it for a batch or two of soap, I decided this one is for food only. The bell is not stainless steel; it's some kind of cast metal that discolors with exposure to lye. Also there are rubber seals inside the mix head, and I fear they are not suitable for being around lye either. And the cost is an issue -- I won't feel bad if the PS or the Cuisinart die early deaths, but the Bamix had better be running strong for decades, as much as it cost my DH a few years ago when he got it for me as a gift.
