He's objectively the best. I absolutely love how he makes up for his lack of raw power with cunningness and intelligence. The fights against the Pillar Men in Battle Tendency were so awesome to me because, while strength did play a part, Joseph ultimately beats them by outsmarting them. Plus, he's just hilarious. His "OH MY GOD," "HOLY SHIT," "OH NO," etc lines in Stardust Crusaders were a highlight of the series for me.
Apparently, Jotaro is the most popular JoJo in Japan while Joseph is the most popular in the West. I have nothing against Jotaro and liked him well enough, but I just don't get how he could be considered better than Joseph. Joseph is like a fine wine; he just gets better with age. Jotaro is just pretty flat to me.