In many cases, OVA anime aren't a core part of the manga. They can offer supplementary content or alternate perspectives, but they don't typically influence the main manga storyline.
Sure, JoJo Part 7 manga is available in English. But the availability might vary depending on where you look. Some physical bookstores or online platforms might have it in stock.
In my opinion, Part 3: Stardust Crusaders has an amazing story. It's about the Joestar group traveling to Egypt to defeat DIO. The journey is filled with various Stand battles, each one unique and exciting. There are new characters introduced along the way, and the development of their relationships and powers makes for a great story. It also has a lot of iconic moments that fans love.
For a Jojo part to have the best story, unique and interesting characters are crucial. In Part 3, for example, the diverse group of characters like Kakyoin, Polnareff, and Avdol each bring their own charm and abilities. Their interactions and growth during the adventure contribute to a great story. Also, the overarching goal, in this case, defeating DIO, gives the story direction and purpose.
Well, for me, the most interesting part is the unique stands in the story. Each stand has its own special abilities and appearances, like Star Platinum with its incredible strength and speed. It makes the battles really exciting and unpredictable.