I often use Teamviewer to access my MacBook Pro from my main mac, and also my families computers to assist them with problems.
Teamviewer on my MBP will use upwards of 46/62% of both CPUs and 58.9mb ram (its a 2009 MBP), while if I use Apples own remote control (I assume its VNC), 'ScreensharingAgent' it will sit nicely between 1.3 to 1.9 CPU % at 28.2MB of ram.
In terms of image and speed, both look exactly the same, I think Apples remote control is even snappier in responding, but maybe its because of the CPU usage.
The situation is even worse when I am trying to help my mom who is using a 2010 Macbook Air that is considerably less CPU performant.
I have set up Teamviewer to optimize speed whenever I connect to any of the computers and I have also ticked all boxes that I thought made sense, even lowering the color amount to LOW (256) and even grayscale without much change.
I also live in Portugal, so, both houses use Fiber optics connections (100mbs or so) and my MBP is even in the local lan, so I know bandwidth should not be a factor.
I have Googled around and I have found other people with similar problems but no real solutions to the CPU problem.