Sinnoh will never become boring for me. Certainly my favourite main-game region so far.
Although, saying that, GenV has much more interesting gameplay and a far better story, so I'd say that Black and White are ultimately superior games to those in GenIV. It's fairly balanced though, as it is with most of the other Pokemon Generations. While I'll be focusing more on the recent Pokemon games, I am chipping away at a Steel-type monorun on Platinum.