Which Zoom lens?

[timmy_650]

I have the Canon EF 70-300mm f/4-5.6 IS USM and I have been thinking about selling and getting the EF 70-200 f4 non is. I am not sure if it is worth the effort and extra money. Or losing the IS.
I have a sigma 135-400mm but the auto focus doesn't work but that isn't a big problem. So I am not too much worried but losing them zoom.
I am using t2i right now but I am hoping to go full frame by the end of the year. I am not sure which way I will go yet.
 

[neuroanatomist]

The 70-300 non-L is weakest from 200-300mm.  The 70-200/4L non-IS delivers very good IQ.  Even cropped to the FoV of a 300mm lens, the 70-200/4L will deliver better IQ.

[Menace]

I used to have 70-200 f4 on my 7d - very pleased and satisfied with that combo. I'd recommend it.

[sagittariansrock]

Losing the IS might suck, though. A used 70-200 f4 IS might not be too much more expensive and will be cover all bases, IMO. And you can always slap on a 1.4x third party TC and still get better images at 300mm@f/5.6 than the 70-300.
Also, the AF speed and noise of the 70-300 was a big bummer for me. I sold it to get the Tamron, which was far better.