I do not consider myself an expert kayaker by a long shot, I just like making careful observations about the way things work, that is what I do for a living. Of course the best paddle will depend how the person and what type of paddling they do. Very importantly it should be smooth on both faces of the paddle, especially the back side, without stiffening ribs, ridges or a big lump where the handle blends into the blade. The shaft should have a shape that lets you know the blade orientation by feel. This is real important, it could mean the difference between staying dry or capsizing because an emergency brace failed when you held the blade the wrong way.
Most inexpensive paddles use round shafts to keep costs down, a poor choice.
Many good modern designs use an oval shaft to do this. I've used both and find merit with each. The traditional native style paddles never off set the blades, and with narrow blades the reason for doing it goes away. I find teaching my kids a lot easier with no off-set, I think it feels more natural to a beginner and gives the student one less thing to worry about. And of course it should be strong to take abuse and preferably as light as possible.