« on: February 20, 2014, 10:14:34 PM »
I have both, have used both extensively, but over time relegated the 70-300 to my Son's use, reasons ??
The 70-300 f/4-5.6 L is a relatively slow lens @ f/4 to f/5.6, not an issue if your in sunny weather, bright conditions, otherwise your constantly looking at cranking the Cameras ISO up. I shoot wildlife, mostly early mooring and late afternoon, it's not that the 70-300 won't work in these conditions, it does, and quite well, but no where as well as the 70-200 with the availability of f2.8.
The 7-300 has a reasonably good range, but note that it will not accept Canon 1.4x or 2x converters, I have read of some people using Kenko 1.4x converters with mixed results.
The advantages of the 70-300 are quite good IQ, light, quite a good range, reasonable price.
the 70-200f/2.8 II L is a bit of a different Lens, if your wanting to do Portraits, other than a more suitable prime, this Lens will work very well for you, have a look at "Bornshooters" portraits on the 1Dx thread, majority I think shot with this Lens. Wildlife with the 1.4x Converter, amazing IQ, with the 2x converter, still very good IQ.
In this range there are few if any Lenses that compare for IQ & versatility.
Only disadvantage that I can think of over the 70-300 would be, more expensive by a large margin, weight. But versatility, IQ can't be beaten I feel.
Another option for you might be to wait if you have the patience until Canon release their new 100-400 f/4-f/5.6, this I imagine will be a Lens worth the money, hopefully, but it could be a 6 month to a year wait going on Canon's past performance of hint re development, declare production started, offer to the Market, on the 200-400f/4 that was about 3 years.