Many gardeners don't know what a lopper is or what it is used for - until they need one. If you find you need two hands to make a cut with your hand pruners, it's time to switch to a lopper. Loppers are basically hand pruners with long handles. While the longer handles will give you added reach to prune higher branches, that's not their true advantage. The handles on loppers give you leverage, so you can pruner can handle larger branches; up to 2" in diameter, depending on the lopper.
The same basic principles and features of hand pruners apply to loppers. You want a carbon-steel blade and the option of replacement parts. There are by-pass, anvil, rachet and ergonomic loppers too.
There will be less stress on your hands when using loppers, since you'll be using both hands to make a cut. But a comfortable grip is still important and some type of cushioned bumper behind the blades will prevent the handles banging together and jarring you.