There's at least two places I stopped.
First time was in the middle of Johto when I felt I "out-grown" Pokemon. Picked right up in the middle of Sinnoh (I guess that's why the new voices never bothered me, because I wasn't invested enough to notice the change).
Second time was when I heard about the end of the Sinnoh League. Tobias is the status quo given character form. I threw up my arms and said "No, I'm done". Only going back after playing the awesome Black & White and learning the anime was also much different (no Brock, less filler, tournament arcs, Team Rocket's role reduced).
White 2 Friend Code: 0777 2090 8695
All about the trading.
Unova Dex Progress: Complete (not counting Meloetta)
National Dex Progress: 340/649