What is considered the number one toothbrush for gum disease?

Technique, not TB: It's not which toothbrush. It's the proper technique and amount of time using the toothbrush and dental floss after meals, not to mention necessary periodontal (gum) treatment by a qualified dentist. That being said, use a soft toothbrush, and make circular movements at a 45 degree angle to your gums and teeth.

Soft bristle: Any tooth brush with the soft bristle is adequate. Do not fall for any gimmick and waste your money. Use the bass technique (short, linear or circular motion, brushing angular and parallel to the gum)! use with regular toothpaste (fluoride such as sensodyne if sensitive teeth). Oral b is a good brand of toothbrush. Make sure it is soft bristle to prevent gum recession.

Electric: I think an electric toothbrush like oral-b or sonicare is what you should get.

See below: There are many choices out there and branding one as best would be unfair. Electric brushes are nice since they reduce your physical labor. In my opinion the technique is much more important than the brush it self. You can properly brush and eliminate gum disease using the worst toothbrush by using the proper technique. See a dentist for proper oral hygine instruction.