Radial is what the "wagon wheel" type is called and it extracts both sides at the same time. The less switching you have to do the better, especially if you are having to extract lots of frames.
If you are going to put out the money for a motorized extractor I recommend going with the next bigger size then what you think you will need if you ever plan (or it even crosses your mind) on increasing your number of hives. Otherwise you will be buying a new extractor every couple of years.
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