It might not be the levers. If you haven't already done so, try this:

Before trying to pry the tire off of the rim, pinch the two tire beads in in together all of the way around. The center of the rim is lower and that allows the tire to become non-concentric with the rim and gives you more room to work with. Some tire and rim combinations are more difficult than others, but MOST of the time I don't need to use a tire lever for either installing or un-installing bike tires.