The Bernette B38 is brand new. It may be hard to find. Our store doesn't have them yet. Prism99 is right about the Bernette is definitely not a Bernina. The thing that makes a Bernina so great is the metal bobbin case, metal bobbin and metal hook with an oscillating hook system.
The Pfaff and Bernette that you're looking at will be about the same -- both have the plastic bobbin case and drop-in plastic bobbin. The bobbin case will jam if you sew heavy fabrics, but will probably be alright for what you are sewing.
If you want an auto thread cutter, you have to get a machine with a rotary hook system. Most drop-in bobbin machines are rotary. There are a few front-loading rotary hook machines that are metal, like the Bernina 180, 200, 440, 560 and 580. Pfaff has some vintage machines that are metal rotary machines. You might consider buying a used machine.