70-300 L or Tamron 70-300 vc

I have never used the 70-300L but have owned both the 70-200L F4IS and the Tamron 70-300 VC.

I really like the 70-200F4IS, I eventually went with the 70-200 2.8 ii, but really loved the 70-200f4 is.

Ultimately, I found that the 70-200 even with the 1.4x was just as sharp in real world testing with as the 70-300VC. I know the test charts show the VC very good, but it was always a little soft for me.

Here's my list:
Sharpness: 70-200F4 wins even with 1.4x
Contrast: 70-200 definitely won

AF: 70-200F4 was faster and more accurate, with the 70-200 + 1.4x the 70-300VC was faster and more accurate:

IS: The VC system seemed much better than the Canon IS, the image didn't drift like the Canon ones do.
Size + Weight: The VC is very small which is nice for sure.
Cost: VC obviously wins especially if you are buying a TC
Build: The Canon 70-200's are pretty amazing build quality

For the dollars the VC is a great lens, but for me, never was sharp enough, or AF accurate enough, and eventually it got replaced.

There is my 2 cents.