Will you do video editing and music recording professionally?
If so, get the 15" MBP or 15" MacBook Pro with Retina Display, as the quad core CPU and dedicated GPU will help immensely.
If it is only a hobby from time to time, and your budget is tight, get the 13" MacBook Pro with Retina Display or 13" MBP if you want.
The 13" MacBook Pro with Retina Display offers more screen real estate, which is important in music and video editing.
But also know, that the MBP line is due for an update with slightly faster CPUs, better integrated graphics and much better battery life in October or November 2013, thus if those aspects are important to you, especially the battery and integrated graphics processor (IGP), then wait.