I couldn't imagine not using a wing-blade.
A lot of guys will argue that a flat-blade paddle does the job, which is true, but even though your work boots also do the job of protecting your feet if you go for a 5km run wouldn't you rather have a pair of running shoes on?
The most important choice for me when choosing a blade is the volume of the paddle. You can get good acceleration and power out of a big paddle but you're going to feel it in your shoulders pretty quickly, unless you're a really big, fit guy. My personal favourite is the Lettman 1 paddle. It's a small volume blade but I prefer to paddle with a higher cadence than with slower, harder strokes. I find it creates a lot less strain on the back and shoulders.
Other than that, most medium volume blades make a solid compromise. I've got a medium volume glass/kevlar composite, which I find to be quite hard wearing but obviously not as rigid as a carbon blade (the more rigid the blade, the more efficient the stroke, you're not wasting energy from the blade bending in the water, which is what happens with the plastic paddles that a lot of guys try to sell you).
Another consideration is solid or split shaft. If you've got a small car like a Polo or such, a split-shaft makes your life a lot easier, although you'll pay an extra R250 bucks. Well worth it, though, as it means I can just leave my paddle in the ski hatch.