The 35L will win in the sharpness category. However less versatility.
Neither is a replacement. Zooms you can always change perspective. For example a "waist up" portrait you can fill your frame at 24mm, 35mm, 50mm 70mm and maintain the "waist up" portrait. The perspective will look totally different one the 24mm to 70mm. The 35L will ONLY have 1 fixed perspective due to 1 focal length. If you have a bag full of primes you are not limited but if you have 1 prime (35L) all of your photos will look the same regarding perspective....yawnnnnnnnnnnnnn. This is where the zoom is an excellent tool.
BUT.....
The 24-70L is a "good" lens and not stellar compared to the newer mk2 version. From what many pre production testers have claimed the new 24-70Lmk2 has similar IQ as a 70-200 f/2.8IS mk2. If this is the case 35mm at f/2.8 on the new zoom will be as good or better than the 35L. The 35L is a great lens but I much prefer the IQ I get from the 24Lmk2 (new canon coatings etc etc).
Pick your lens based on needs. If you need fast glass you need primes. If you need versatility the f/2.8 zoom will suite your needs.
out of the two I prefer the 35L for available light shooting and for events the 24-70L is my goto lens. If I'm stuck requiring fill flash the 24-70L is much preferred since f/2.8 will be plenty fast in most cases with flash bounced fill. Small studio setups shooting young children the 35L it annoy you!!!! The 24-70L will be able to keep up since you can zoom.
I have both for a reason.
joelmarineau wrote in post #14835789
I am thinking of selling my 35L to grab a 24-70L.
Many of you have sold your 24-70L after buying a 35L, I use the 35L for many shots as my day-to-day lens and I really like the IQ and Sharpness of this lens but I would like it to be sometimes wider for landscape/videos and sometimes longer for portraits. The 24-70L seems to fit right for my usage but I wonder if I will see a big difference in IQ and
Sharpness that may make me regrets my move...