"I'm looking to improve my strapless riding
then its Mancora (or more importantly Peru) hands down. but....
I've spent 3 months at both cumbuco and Mancora. Mancora does get busy. Even if there aren't lots of kites there are lots of surfers and some of the worst snaking i have ever seen - expect bad etiquette. Personally I rate Pacasmayo and Lobitos - not far from Mancora for kiting. Mancora is one wave on one point, Pacasmayo is a wet dream but Mancora, more importantly the town will keep you interested. Not much nightlife in pacasmayo or Lobitos. There is also really good TT riding at Tres cruces near Lobitos and i kited 90% of the time there alone.
I am not biased , i have no affiliation with any company. Cumbuco and Northeast Brazil is stunning though. Thinking about the whole package (accommodation, food, nightlife, meeting other kiters etc) i would choose Cumbuco but if you seriously want to improve strapless then Peru has to be the option - world class waves. Peru is much cheaper than Brazil also.
... Did i mention Brazilian girls