Almost every Emacs user knows that you can use Esc as the Meta key. It started because keyboards between, say, the Space Cadet keyboard and modern keyboards didn’t have an Alt key to act as Meta.
The practice lives on. Guys like Mike Zamansky started with keyboards lacking an Alt key and continue using Esc out of muscle memory. I somehow missed all that and I’ve always considered it a bit odd but dismissed it as ingrained muscle memory as in Zamansky’s case.
Bozhidar Batsov has a different take. He started using the Alt key for Meta but has found that he likes using Esc more.
Batsov makes a cogent argument for preferring Esc and I found myself almost convinced but I know that at this stage it would be really difficult to retrain my muscle memory. It’s not just Alt → Esc. Rather it’s all those Meta + ... bindings that I think of a unit. I don’t think of them as Alt and then some other key(s) but as a single binding so switching to use Esc would mean relearning many, many bindings.
On the other hand, you don’t really have to choose. It’s not a configuration item: both Alt and Esc work out of the box so you can use either or both. Of course, that adds even more complexity.
In short, I find Batsov’s arguments compelling but not enough to go through the pain of retraining years of muscle memory. But I do have a new appreciation for those who use Esc.