All of them seem really similar, but some are still slightly higher % fiber and some may have lower GIs (I presume lentils are easiest to digest but they also seem the “simplest”)
They vary in their nutrient profiles, fiber content, phytochemical composition, etc.
Rather than focusing on the one “best” it might be prudent to aim for a wide variety to get exposure to as many different phytonutrients as possible. That’s what I do.
But sometimes I lean towards the less gassy ones (lentils, split peas, adzukis, etc.).
Digestive enzymes and beano can help your tolerance. Eating smaller quantities per meal is also good. At almost 60 I can no longer consume massive quantities without issues like I could when I was your age.