So sorry for continuing a bumped dead thread, this topic fascinates me.
That said I have to say the 4kids dub was good, had some problems occasionally with script, but the performances especially in the later seasons in their run were really good. I always liked Veronica Taylor, Eric Stuart, Maddie Blaustein, Rachael Lillis, Darren Dunstan, Marc Thompson, and Wayne Grayson in the 4kids Run.
The Pokemon USA side (Taj) was bad, really bad. Whoever was in charge of voice direction didn't do a good job I'm afraid, as a kid I found most performances very unsatisfying and hard to listen to, even today I still can't ever get as much enjoyment rewatching the Battle Frontier, outside of the ugly lighting the season picked up in comparison to the start of AG, the voice acting had some of the worst performances I've heard of anything I've watched, and I can only blame how fast production was moving and the not so well handled voice direction.
After that point when DuArt picked up Pokemon voicing, the quality got so much better thanks to Tom Wayland being the best person to be in charge of directing voices, I will say it's hard for me to chose now if I like Veronica or Sarah as Ash's voice, because they are on par with each other really, without taking into consideration how bad was Sarah thanks in part of Taj's lackluster directing she got. I genuinely found the voice acting handled pretty well in the DuArt era, though I can't say for sure how it was handled during X and Y to Sun and Moon since I have yet to watch Pokemon from that era to say much.