I would happily have Morphy in the conversation too, because he was so far ahead it's simply mind-boggling. He made his opponents, often the strongest players of the time besides him, look like idiots.

If we're judging only by strength relative to contemporaries, I think Morphy would take it.

If we judge only by absolute strength Carlsen at his peak is probably it. For some mix of the two, all the ones mentioned are potentially valid picks, and I'd include Lasker in that group as well.

Tal probably would've been if he was a lot healthier, but he doesn't make the list in an unfair world, though I'd be amiss not to at least mention my favourite historical player :)