I've got a 24-105 f4 and recently added a 70-200 f2.8 IS L MkII. I got the 24-105 with my 5D2 as a kit lens and it's spent a lot of time on the 5D2, a 7D and my 5D3. I really like having the crossover just in case I want to shoot between the 70 and 105 but haven't time to swap lenses. The 24-105 is a very good lens with great IQ and good AF speed and accuracy and the IS is a godsend at times too. Unless you need the f2.8 for specific reasons then the 24-105 is a great introduction to L lenses.