Depends on what you're building, honestly. I think that it's easy enough to get a site running entirely on PHP--well tested, well supported, architecturally so

Depends on what you're building, honestly. I think that it's easy enough to get a site running entirely on PHP--well tested, well supported, architecturally sound, and rewrite services into <noninterpreted-language-of-choice> as you hit performance bottlenecks. If performance is absolutely critical to your app, then you may consider writing everything in Java/Go/C++, but it's pretty brutal for doing templating and whatnot. Besides, once you generate the page, there's a good chance you're going to cache a good part of it anyhow!