The Touch anime is largely faithful to the manga. There are a few chapters and scenes it doesn't cover across the entirety of the series, and a few scenes it added in (like Minami's gymnastics competitor in her same club and her not winning her regional tournament), but more or less the anime does a good job.
The problem starts at the ending of the anime. The anime covers up until chapter 247 of the manga, right before Tatsuya has a fateful encounter with an idol, then just makes up its own fictional ending and has done with it all. The manga has a much better ending. Our hero goes to Koshien, has a date with an idol, confirms his feelings for Minami via doing so, goes and confesses to her right before she performs at the inter-high, after which she wins the inter high, and he wins Koshien, then it shows him studying hard to get into the same college as her so that they can live happily ever after.
This seems to me to be a much more thorough and complete ending than the anime, which just leaves off on an ambiguous and meaningless note. Furthermore, it's also a much better ending than the filler nonsense movies set after the ending of the anime, which completely pervert the main character's character in order to add in unnecessary new drama. Watching those two movies is no good, they're worthless. All you can do is go ahead and read the remaining 10 chapters of the Touch manga, put the manga down, and breathe a contented sigh of 'God is in his heavens, and all is right with the world.'
Why didn't the anime cover the manga all the way to the end? It's a mystery. I assume it had production schedule problems and ran out of air time, or whatever. But it's pretty miserable for such a famous series to cut off just 10 manga chapters before the ending. The people who animate these shows aren't very smart, are they? You make an anime series over 100 episodes, but don't animate the ending of the show by adding in just five more. Then you go and make two anime movies after the series ends, and instead of using this opportunity to animate the remaining 10 canon chapters, they go off on a total filler tangent and attempt to ruin everything with their own dumb, nonsensical storyline which casts Tatsuya as an adulterous scumbag.
Oh well, enough of that. The point is people should watch the Touch anime, then read chapters 247-257 of the manga. The deviations before then are minor and forgettable, but the deviations after that point are ludicrous. Combine the two for the full Touch experience, and everything should work out well.