Molle, I find it extremely versatile although if I'm honest I have a couple of vests that I have set up "just so" and rarely change pouches on them. However the molle system did give me a lot of flexibility trying out different configurations until I found what I worked for me. I tempted to build a sew on rig based on my favourite loadout but I don't think the small saving in wieght/bulk is worth the trouble & I occasionally swap 5.56 mag pockets for 7.62 ones.
I can say I've ever used a modular panel vest. I know a several manufacturers have produced different (probably incompatable) systems over the years but the limited design of most panels didn't interest me or seem much of an improvement over issue webbing.