Murray is small? Huh. I'd say that 6'1 - 6'3" is about average for a tennis player. There are definitely worse serves than his of players in that height range - if we're talking second serve, Troicki's is much worse.
Of the tall players, worst serve is Cilic. I just don't get why you'd serve like that when you're as tall as he is.
Best serve for a shorter player is Almagro. I am amazed at how much that serve can do, especially on his favored clay.