Apple Thunderbolt or HDMI for external monitor Is there anybody who can answer me this question?
I have a Macbook Pro Retina 15" quad i7 etc and I use some programs/applications wich need a lot of cpu and also the macbook heats up like hell. 

I want to extend my display with a 23 or 27 IPS monitor.
Which is the best way, is it through HDMI or Thunderbolt to DVI or VGA adapter.
The main thing is that I use almost all the resources/performance to run those programs..so ...which of the two options does not affect my CPU/RAM and graphics performance because I don't have any left.
Adding another monitor cannot be anything other than more resource-intensive - every pixel takes resources to drive it &amp; draw to it.

The 15" Retina screen resolution is 2880 x 1800
A standard 27" screen is 2560 x 1440 - almost doubling the number of pixels you're asking the machine to draw.
A 27" Retina 5k screen is 5120 x 2880 - almost four times the screen area you already have.

To come closer to actually answering your question…
In order of personal preference, I would choose
Thunderbolt > DisplayPort
HDMI
DVI
I would avoid VGA entirely these days.