Are you going to be writing the majority of the code? If so, try out both languages for a few days each and see which you like better. Spending a week choosing

Are you going to be writing the majority of the code? If so, try out both languages for a few days each and see which you like better. Spending a week choosing the right tool for the job will save you countless hours in the future. If you're outsourcing the development then you shouldn't be concerned about which language is used. You should be looking for a team of developers who know what they're doing and have experience building systems similar to yours. Performance and scalability shouldn't be factors when choosing a language, either. Good caching and a delivery network like Akamai or CloudFlare will be more than enough for most large websites. I work on several large (100k+ visitors/day) websites that run on PHP - we get by just fine by caching the hell out of everything on multiple levels (web server, traffic manager, Akamai). My advice is to focus on the end product, not the implementation. Don't get caught up in which technologies to use, or you will lose sight of what you want to create.