Please define "webhost". For a lot of people, that means "PHP hoster", and that sort of limits your choice of languages to 1.
For a large webapp, I would definitely take something that runs on the JVM (assuming that your definition of "webhost" includes some shop that accepts .war files for hosting - I usually self-host on virtual machines and run the Play Framework because it is so much easier). On the JVM, you have a choice of frameworks and languages - and again check out Play - and here it starts depending on language skills, specific needs, etcetera. Scala would, for a large app, definitely be on my shortlist these days.
Note that I say "JVM", not "Java". I think the JVM ecosystem rocks - you will probably find a site that takes the standard .war file format to host, if you need a library it is usually there, performance is top-of-the-line. Java as a programming language is so-so, but luckily there is choice these days.
Also, a lot depends on your skills, your preferences, etcetera. I'd say that Python, Perl, Ruby, C# all are very viable languages to build large websites. What development languages do you prefer? At the end of the day, that's a big factor in speed and ease of developement...