Prioritise repositories in Ubuntu

We have a few PPA sources on some of our servers which we stick into /etc/apt/sources.list.d . Some of these repos provide same packages (in terms of names) but different versions and possibly different binaries. Is there a way how we can PRIORITISE one repo over another ?

I gave a read to apt_preferences tutorial but it could not be more obscure and didn't find the answers for my question. Here is the situation. WE have the following sources:

$ ls -l /etc/apt/sources.list.d 
total 12
-rw-r--r-- 1 root root 66 Jan  2 16:50 nginx-source.list
-rw-r--r-- 1 root root 84 Jan  2 16:49 ruby-ng-experimental-source.list

where nginx-source.list:

deb     http://ppa.launchpad.net/nginx/stable/ubuntu precise main

and ruby-ng-experimental-source.list:

deb     http://ppa.launchpad.net/brightbox/ruby-ng-experimental/ubuntu precise main

Both of these sources provide nginx-full package of different versions etc. When I list the priorities ruby-ng-experimental-source.list is on top of output hence nginx-full is installed from that directory:

$ apt-cache policy nginx-full                                 
nginx-full:
  Installed: 1:1.2.3-1~38~precise1
  Candidate: 1:1.2.6-1~43~precise1
  Version table:
     1:1.2.6-1~43~precise1 0
        500 http://ppa.launchpad.net/brightbox/ruby-ng-experimental/ubuntu/ precise/main amd64 Packages
 *** 1:1.2.3-1~38~precise1 0
        100 /var/lib/dpkg/status
     1.4.1-1ppa0~precise 0
        500 http://ppa.launchpad.net/nginx/stable/ubuntu/ precise/main amd64 Packages
     1.1.19-1ubuntu0.1 0
        500 http://mirror.rackspace.co.uk/ubuntu/ precise-updates/universe amd64 Packages
     1.1.19-1 0
        500 http://mirror.rackspace.co.uk/ubuntu/ precise/universe amd64 Packages

How do I prioritize repo listed in nginx-source.list ?

I tried something like this:

$ cat /etc/apt/preferences
Package: nginx-full
Pin: origin http://ppa.launchpad.net/nginx/stable/ubuntu
Pin-Priority: 1000

Package: nginx-full
Pin: origin http://ppa.launchpad.net/brightbox/ruby-ng-experimental/ubuntu
Pin-Priority: 100

But that has changed priorities of ALL sources - or something like that ?

$ apt-cache policy nginx-full  
nginx-full:
  Installed: 1:1.2.3-1~38~precise1
  Candidate: 1:1.2.6-1~43~precise1
  Package pin: (not found)
  Version table:
     1:1.2.6-1~43~precise1 1000
        500 http://ppa.launchpad.net/brightbox/ruby-ng-experimental/ubuntu/ precise/main amd64 Packages
 *** 1:1.2.3-1~38~precise1 1000
        100 /var/lib/dpkg/status
     1.4.1-1ppa0~precise 1000
        500 http://ppa.launchpad.net/nginx/stable/ubuntu/ precise/main amd64 Packages
     1.1.19-1ubuntu0.1 1000
        500 http://mirror.rackspace.co.uk/ubuntu/ precise-updates/universe amd64 Packages
     1.1.19-1 1000
        500 http://mirror.rackspace.co.uk/ubuntu/ precise/universe amd64 Packages

Thanks for the answers!