They both have their advantages / disadvantages, they are both very compatible and very fast. 1964 runs like a bullet but lacks proper plugin support, i.e they relay on other plugins. Project64 isn't as fast as 1964 but has a proper lineup of plugins, possibly the best I have ever used, and very good support. If 1964 had better support, i.e ini's, faqs they would be on pair with Project64.