What type of software engineer has the most demand and greatest salary?

Short answer is: The one who can negotiate well. 15+ years in professional software

development, I have seen many of both:

• Brilliant engineers either not aware of their value to the company and / or cannot negotiate a good salary due to God knows what, lack of social skills let’s say.
• Average engineers who are great at what to ask, when to ask, who to ask and how:
• They get prepared. They practice their talk. They already know how to reply when they’re told ‘Oh but your peers are getting lower than you?’, for example.
• They’re good at their timing. It’s probably a better idea to ‘demand’ something after you proved yourself and / or achieved something.
• They’re social. They tend be close to the management. At your company’s Xmas dinner, who is drinking, talking and laughing with the managers, when others try to avoid even an eye contact?
• They create alternatives. At the negotiation, it almost always ‘helps’ to say ‘well you really love the company and want to stay BUT also has a great offer from another company’.

List can grow forever. Second group tends to do better on average.