What is the difference between a digital camera and a reflex digital camera? Which is best?

Digital or not, in all reflex cameras, when you look to the viewfinder, you can see the image which directly comes from the lens. In another words, you will see the same image captured by the film frame or the digital censor. Reflex digital cameras are called SLR (Single Lens Reflex) Digital Cameras. When you compare them to compact digital cameras, of course, SLR's are more, and some models are the most professional cameras.

A digital camera is a capture images on a Chip inside a camera.A reflex is like a Polaroid that come out of a camera. The digital camera is the best to me.

Digital Single Lens Reflax cameras are much better. They let you use a wide variety of lenses, and they operate much faster. These are the cameras that you see pros use. For example, with a professional digital SLR, you can take 8 pictures per second - with a compact camera, you're lucky if the camera can do 3.
The advantage of regular digital cameras is that they are cheaper and usually very small.

it's difficult to say which is best, depends on what you want to do. A digital single lens reflex is more capable, in terms of giving you more control, choice of lenses etc and is better most of the time. But a lot of people will also have a smaller digital camera to keep in your pocket for grabbing snapshots etc.