>>539912283/3
By any chance are you also watching the movies and specials alongside the episodes? If not, there might be some you probably should.
For the movies, the first 4 are all highly recommended in quality (by Pokémon standards) and/or tying the plot to the series. After that, the only ones I can really recommend are 5, 8, and 21. If you've seen the 2nd movie,
you've basically seen movies 5 - 19. 20, 21, and 23 are in its own continuity and 22 is a remake of 1.
For recommended specials pertaining to the original series (Kanto and Johto), there's Mewtwo Returns, The Legend of Thunder, and the specials that aired during AG on the Weekly Pokémon Broadcasting Station in Japan which became part of Pokémon Chronicles in the dub.
When it comes to sub vs dub, I'm also recommending what the other anons have said; if you go dub, switch to sub after Advanced Battle. I also highly advise to go sub when watching The Legend of Thunder and any other special in Chronicles as the dub quality for Chronicles is worse than the series and movies.