The m50 will stay on your head well, buy at the same time it can have a tight clamp. The ear pads material and the tighter clamp can also make your ear sweat if you are walking outside after 20-30 mins depending how hot it is. They are some what big for portable, but a good size for full size portable. They are built well so no need to worry about hurting them, they do fold pretty small and comes with a bag. The downfall for me as far as portable is the long wire, straight cable version seems too long and the coil version cable can be weighty when wearing them. Look wise, most bigger headphone will look some whAt off in my opinion, but the m50 do look simple enough as far as styling. Oh they are somewhat heavy for portable and I think the swivel ear cup can be some what clumsy for on the go, don't get me wrong the way how the swivel and claps works great but for me on the go should be slightly simpler. They isolate well and don't really leak either.
Overall, I think they are okay for portable, nothing great. In my opinion if you are walking with them consider something smaller, lighter with shorter cable. If you are going to carry them to a certain destination and sit down for a listen then they might work.
No comment on the akg as I never tried them.