I had a Sunbeam Mixmaster many years ago when I was a newly married. I worked fine for a few years, but finally pooped out under the strain of the heavy use I gave it. And of course - it died right in the middle of preparing food for a large holiday dinner. :(
I got on the phone and called my husband at work, and told him I wanted a KitchenAid for Christmas, and I wanted it today so I could finish what I started.
I had it set up within the hour, gave him the bill with a bow on it,
and have never looked back. More than 25 years later, it's never had a hiccup, in spite of the workouts I give it.
Having owned both, my strong opinion is that there is no comparison between the two. For an occasional cake, the Sunbeam will do just fine, but if you you use a mixer a lot, especially for breads and doughs, it won't hold a candle to the KitchenAid.
Evern Julia Child, who never endorsed products, told folks to buy the KA. In her "Mastering the Art of French Cooking, Volume 2" she included a sketch of the KA and wrote "We strongly suggest you buy the type of mixer pictured here." If you have the book, read page 539 for her reasons.