What camera is best for concert photography?

I don't care about the size because i have been using Canon EOS REBEL T3i at concerts already

You really need one that performs well at high ISO settings as well as one or two fast lenses.

That would mean something like the Canon 5DS, but remember, you will need to replace any of your Canon EF-S lenses since they can't be used on Canon full frame cameras.

I use a Nikon D800e when shooting performers under stage lighting coupled with either a 24-70 mm f/2.8 or 70-200 mm f/2.8 depending upon whether I have an "All Access" media pass or not The best high ISO Canon body (ignoring the 1DX) is the 6D. Paired with a fast prime, it should give you decent results in nearly any concert situation.
The 5DS and 5DSr are definitely NOT good high ISO options. I would look at the new Sony A7S II which has the best high-ISO performance. You will also need fast glass with apertures of at least f/2.8. Since you can adapt your current lenses to fit any of the Sony alpha mirrorless cameras, I'd go with a Sony.

If you want to stick with Canon, then use this tool to see which camera has the best ISO performance: http://www.dpreview.com/...f=mainmenu" rel='nofollow' class='ext_link'>http://www.dpreview.com/...f=mainmenu The one held by the event organizer's official photographers. Other than those, none whatsoever.

The best high ISO Canon body (ignoring the 1DX) is the 6D. Paired with a fast prime, it should give you decent results in nearly any concert situation.
The 5DS and 5DSr are definitely NOT good high ISO options.

I would look at the new Sony A7S II which has the best high-ISO performance. You will also need fast glass with apertures of at least f/2.8. Since you can adapt your current lenses to fit any of the Sony alpha mirrorless cameras, I'd go with a Sony.

If you want to stick with Canon, then use this tool to see which camera has the best ISO performance: http://www.dpreview.com/reviews/image-comparison?ref=mainmenu

The one held by the event organizer's official photographers. Other than those, none whatsoever.