Anyone who was around in the 90s when the series was still running will tell you that
Morphz was undoubtedly the best one around, simply because the owner (Jeff) was in direct contact with K.A all the way until the end. He provided us with a lot of behind the scenes info, as well as plots and inside scoops for upcoming Animorph books and promotions, both on the website and in the forums.
There were also very dedicated and popular Animorph websites such as
Ani-News,
Escafil Device,
MAS, and
Ziana Astralo's Animorph Galaxy. Those are the ones where practically
everybody went to.
There were also many other good ones like:
Animorphs Plex,
Animorphitis,
Animorphans,
Jake's Animorphs Site, and my old (and now shut down) website
Aximlli's Animorphs.
My old website is now replaced with
Hirac Delest as morfowt mentioned above, which is an archive project where I try to update every so often with as much data as a I can find for Animorphs from the old days. So far it's turning out really well and I've seen a lot of support from fans who try to help out.