Postures are something which I have thought a lot about and experimented with.
I don’t care to argue about what is more pious or appropriate. I think that is somewhat subjective to each individual.
However, I do think that some positions better serve to center oneself and call the body to attention, rest, or what have you.
As an altar boy, I was taught to use the more formal and traditional postures. This included stuff like the “praying hands” posture, one hand on the chest while holding an object (including things like swinging the thurible and presenting cruets), both hands flat on the lap while sitting up straight. (Our training went so far as to things like proper ways of making various bows, how to hold a processional cross or banner, how to hold candles, how to carry a chalice, how to walk along with a priest holding his cope open, how to grasp and place a humeral veil upon his shoulders, wearing gloves to hold a crosier or mitre… you name it, we knew it and did it.) I was one of the only kids to actually stay fully true to the hand postures most of the time, despite peer pressure. At first, it is uncomfortable and seems tedious. But you get used to them. Now as an adult (my serving days long gone, though I can still do all of this stuff in my sleep) I still use these positions regularly.
I find that there is a very real and sensory effect and awareness upon the body, mind, and soul that such postures tends to bring about. Similarly, I believe that the posture which some religious and monks use of both hands at chest level flat (palms inward) with elbows pointing out is a worthwhile one. And when one is standing at a less formal moment, the “at ease” position is very useful.