Posted 23 February 2013 - 12:56
At work we have web applications written in Ruby on Rails 3 using redis for caching which easily serve 5,000,000+ hits/day (page, not unique) hosted on a single 2.8GHz Quad Xeon, 16GB RAM server. The only site we have written using the Laravel framework gets 750,000+ hits/day and handles it fine.
Both will scale as long as you write your code with scalability in mind (e.g. potential to cache expensive queries, ability to split the application across load-balanced servers, etc). Pick the one you're most comfortable with, I much prefer Ruby to PHP so usually I go with Ruby on Rails. Remember though, don't worry too much about premature optimization because most sites never take off, you can always spend time optimizing the code base once the site starts getting a lot of traffic (if ever).