I enjoyed writing my answer to "Why did Tony Stark design the Hulkbuster armor?", in which I take a small look at Bruce Banner's relationship with his alter-ego, The Hulk, in order to explain why he would have helped Tony Stark create the Hulkbuster suit.
I also enjoyed reading @cde's answer to "How did Veronica get from Earth's orbit to Wakanda in a matter of seconds?", which uses real life maths and physics and a knowledge of space-y stuff in order to prove that the Hulkbuster suit could have reached Tony within a few minutes.