Since I don't think Pokemon counts as real anime, I'd have to say Dragon Ball Z. The Frieza Saga and the Cell Saga were running on Cartoon network at the time, and I would watch them whenever I could.

After Dragon Ball Z stopped airing on Cartoon Network and the Pokemon TV series no longer was cool, I didn't watch anime for years until Rorouni Kenshin came out. I watched about a dozen episodes of that (good show!), but that's all the anime I've ever seen.