IMO his greatest accomplishment by far is Space X, from an engineering perspective it's the one that seems the most impressive and hardest to achieve.
Tesla is impressive but it seems more like the success of a vision, making electric cars look cool and inspirational, not "like a real car but eco-friendly and boring". Technologically speaking are they really ahead of the competition?
Meanwhile the Boring company and especially Hyperloop fail to convince me. For the former it's mostly that I don't see what he's bringing to the table. If digging holes underneath large cities is so great why did we wait for him to do it? Why does it seem to be such a huge pain when everybody else does it but it would be cheap and easy for him? What's the secret sauce? Where's the innovation? It's not like we didn't know how to dig tunnels before Musk. They've been extending Paris Metro line 14 into the northern suburbs lately and it's a long, expensive and complicated process, both technically and administratively. What would Musk do better?
For the hyperloop it's almost the other way around: the innovation is obvious but what's unclear is if it can work in practice and actually be useful, so I think that would be a better situation to argue that "he's got Space X to work, why not Hyperloop?"