With recent price drops Canon’s “budget” full frame camera is close in price to the newer 70D.  At first glance they look pretty similar and size and shape and both offer 20MPs - but this is where I need to pause and remind everyone that a number like MP tells so little that it is often worthless to compare. IN a day when we have cell phones shooting 20-40 MP we must consider the size of the sensor and a full frame sensor is significantly bigger than the APS-C sensor found in the 70D.  Let's look at the similarities

• Both are about same size and weight - 6D is just a little heavier.
• Controls are very similar - top LCD and rows of buttons virtually identical
• Both have Wifi - remote triggering or connectiing to smartphone or laptop for downloading images.
• LCD Screen is same resolution

Differences

• 70D screen is touch sensitive and articulating - I find both to be extremely useful in a variety of situations and no i never accidentally trigger the touchscreen.
• 70D has a popup flash -nothing to get excited about but it is still nice to have and can trigger off camera flash using. You will need to buy an external flash for the 6D- best budget flash is Yongnuo $90 bucks which is going to give you much better results but it is something you need to buy and carry around
• 70D has a button near the shutter Af area selection - points to greater control over AF with better options vs the 6D
• 6D has just 11 AF points and only center is cross type vs 70D with 19 AF points all cross type.  It is important to note that the center AF point on the 6D is much better in low light.
• 6D has an additional custom mode on the dial (2 custom modes vs 1 C1 on the 70D)
• 6D has GPS - nice for traveling, can impact battery life negatively. 70D is compatible with external GPS Device 
• 70d can fire off 7.5 fps vs 6D is around 5 fps.
• 6D has a max shutter of 1/4000 and 70D 1/8000.
• Flash sync speed 1/180 on Canon 6D and 1/250 on Canon 70D - this isn’t anything to get hung up on but it is somewhat disappointing that Canon made this choice to limit the 6D in this way.

 Image Quality - The 6D with its full frame sensor really produces beautiful low noise high detail images, even at the upper range of the ISO limit.  70D is an excellent crop sensor camera but less detail in images and as light levels drop the noise does increase compared to the 6D.  Really it comes down to performance vs image quality. The 70D is fast, super user friendly and cheaper with cheaper lenses available.   The 6D is slow but produces lovely images - you pay more and you will pay more for lenses as the 6D needs EF lenses which typically are more expensive.Watch my 70D Review | Buy the Canon 70D from Amazon | Canon 70D from B&H Photo Watch my 6D Hands On | Buy the Canon 6D from Amazon | Canon 6D from B&H Photo  Watch my Canon 70D vs Canon 7D Mark II