i have an FBO with two color attachments in my OpenGL 3 application.
Both buffers have the same dimensions and precision. I don't use any mipmapping and probably no multisampling.
The first attachment is filled by a rendering pass.

Now, i want the contents of the first attachment simply copied into the second one to be used in another render pass.
This needs to be done each frame.

What is the fastest way to accomplish this?

I could use glBlitFramebuffer() or I could use MRT - write the same fragment during the first pass into two color attachments.
What about glCopyTexSubImage?

Any suggestions, comments?