I mostly used a mixture of new and old Pokemon. In Sinnoh, some of my playthroughs used Quagsire or Golduck as my Water-type. In X, I had two old Pokemon (Charizard, Roserade) in my main story run compared to 4 new 6th Gen Pokemon (Greninja, Sylveon, Pangoro, Meowstic). Moon was mostly Gen 7, while in Ultra Moon I did use Magnezone due to its great defensive typing and general advantage against most major opponents. In Alpha Sapphire, I mostly only used Hoenn Pokemon.
My teams tend to usually include a Grass/Fire/Water trio as well.