easy pinatas to start with or to finish up the 20 different species needed for this achievement are the domestic pinatas. You can buy them in bulk and all in one go if you're wanting to get this achievement quickly. Just buy 7, wait for the master romancer award for that species to appear, and then sell them right back. You'll lose a little money, but think of it as money that would have been spent on the animal house, and on all the things required to make them romance ready, and then on successive romance candy.
And you save lots of time and effort. Unfortunately, there aren't enough domestic pinata to do the entire achievement. But if you stick with the lower level pinata, the romance games aren't too difficult. And then you can use all the multiple of the lower level pinata towards the residency and romance requirements of the higher level pinatas that need to eat the lower level ones.
A GOOD WAY TO GO ABOUT DOING THIS IS MASTER THE PINATAS THAT EVOLVE LIKE THE LIKATOAD AND THEN EVOLVE ALL 7 OF THE PINATAS THAT WAY YOU GET 2 AWARDS IN 1. ALSO THE FLUTTERSCOTCHS COUNT FOR 3 WHITE, PINK, GREEN, DONT WORRY ABOUT MAKING 14 WHITE BECAUSE ANY TIME A GREEN OR PINK HAVE AN EGG IT IS A WHITE FLUTTERSCOTCH. SERPANTS ARE A PAIN BECAUSE YOU CAN ONLY EVOLVE BY HITTING THE EGG.