Question: I find myself spending a lot of time setting up new servers. I always have the same exact software stack:

nginx
mysql
php + php-fpm + xcache
memcached
munin

I pull all the configuration and init.d scripts from my github repo.

All my servers run Debian. My first step is usually apt-get update and apt-get install vim (and other basic packages).

Would Capistrano or Puppet be capable of automating this process?
If they both are, which one would be more suited for the job?

PS: I would prefer Capistrano because I am comfortable with Ruby.

Answer: 
Puppet would be ideal for this. Puppet provides you with a declarative language to describe the configuration of each server, including packages, services and configuration files. Puppet provides a strong framework to describe the dependancies that each component has on each other, which allows your to build modular configuration files that describe *how* to take a base image and turn it into a server ready to handle a particular role.
That does sound like a perfect application of Puppet. If it'll help, I've written a series of short tutorial articles on Puppet for complete beginners, which covers installation, getting up and running, and managing your first Puppet resources:

[Puppet tutorial](http://bitfieldconsulting.com/puppet-tutorial)