I have been considering one of these to replace my Tamron 28-75 as well. Should I pickup a new copy or go for one of the good looking used ones on ebay? I would use it on a 5 and 7D.Personally I'd go for the 24-105mm L over the Tamron in a minute. I've shot that lens and it never compared to my 24-105mm. Have you tried AMFA on your 7D with your 24-135MM? May make a difference.
I have the Canon 24-135 is usm that actually takes beautiful shots on my 5D but not as much the 7D...makes no sense to me.
Or should I just stick the with 24-135 since I already have it.
I'd go for the 24-105mm over the 24-135mm too. I'd sell them both and pick up a new or almost new 24-105mm. Personally I like new. Sometimes there are some excellent almost new copies out there. Always ask the seller for the date code though and only go for the newest. When buying used, I always buy as new as I can get...
Oh btw, I've used the 24-105mm L on both my 5d Mk III and my 7d. It performed flawlessly on both...