There is no universal answer other than some characters are stage dependent. For example, Samus and Sheik's SH can reach the lower platform on YI without need for waveland. While Falcon can FH backwards to reach the top platform of YI. However, in most cases for characters and stages its FH -> waveland gets you the fastest speed. I never know of a situation to double jump -> waveland to a lower platform.
As for speed, yes, there are some differences for characters about 2nd jump or FH being faster. The best example I can think of is Peach. Her double jump simply does not reach the same height as her FH does for its speed. 2nd jump is much slower.