In many people the hips are too narrow to make full lotus possible sans
knee injury (runners are often in this category), and in some cases even the Burmese style is knee-endangering. In these cases, the best choice is a meditation bench that allows for a seiza
-like posture but with the weight held by the bench rather than the legs.
Western people generally are simply unaccustomed to the lotus postures, and I think it's unhelpful to consider a seated yoga posture to be a meditation prerequisite. Having said that, however, the choice to use a chair isn't great either because the knees aren't generally below the hips, and such a posture isn't as easy to maintain over long periods due to improper maintenance of lumbar lordosis (the natural supportive curve of the spine).
So a bench strikes me as ideal for many. You can make a serviceable bench with just a couple of bricks and a board. It can be well-worth the time saved avoiding attempts to pretzel up, and the motivation to meditate becomes remarkably easier to come by when you know that the posture - in and of itself - isn't going to be an arduous test of endurance.