Obviously this differs with height.
I recall in Federer's peak days, his weight was in the 170 lb. range. Nowadays he is 187. I think he has chosen to add muscle in his later years, perhaps to offset his loss of speed.
Nadal is 188, and has been for much of his career.
Djokovic, however, is only 176. This allow him to be quicker around court than those two,
Djokovic is an inch taller than Fedal, but weighs a good 10+ pounds less.
Tsonga, meanwhile, is the same height as Djokovic, but weights 200, 24 pounds more than Nole
As for shorter players, Ferrer is 5'9'', 160. Nishikori is 5'10'', 150. Laver back in his day was 5'8'', 147. Ferrer has got more muscle than Nishikori and Laver, but the latter two can move quicker. Ferrer has more power, though.
Maybe it is genetic thing? Ferrer and Tsonga are more bulky for their heights cause their bodies are just made that way? While Nishikori and Djokovic for example have a slight frame, exchanging power for speed.
What say you? What is the optimal weight for tennis?