I've seen this question posed a million times, but I'll resist the urge to skip this post and... what the heck, jump right in!


I think the choice boils down to your subject matter and the overall pace under which you'll be shooting.


If you're shooting events and groups of people the 24-70 will serve you well, even on a crop body.


If you find yourself needing to zoom in quickly on a single individual, the zoom will be ideal for portraits.


I'm not sure why people recommend primes for fast paced event coverage. Variables change too quickly to be limited by a single focal distance.


The 16-35 would be nice to have on a second FF body for extra wide coverage in the event that it's needed. But if your subject is close to the camera their face will distort resulting in some unflattering pictures. On the contrary, the compression on the long end of the 24-70 will give you some very attractive close-ups.


BTW, it may be that I have no interest in landscape/interior photography (I primarily photograph people) but I have almost never needed to shoot wider than 24mm on a crop body. If I did it was because I was in a very tight room, my back was up against a wall, and I was dealing with a large group of people. I have tried the Nikon D3/14-24mm and as impressively wide and sharp as that lens/body combination was, I'd still have no interest and snapping pictures of my friends and family as I would find the pictures too... "documentary", if that makes sense.


Regarding other's posts about fast primes - they will stop low light action, yes. but lighting is not always ideal and your subjects won't always be lit properly. Plus wide apertures produce very shallow depth of field. This effect can grow tired quickly and can make focusing much trickier in the mid-focal range. Ultimately, you'll need flash and you'll need ISO1600 or higher. Balance your flash fill with your ISO and you'll find you can manually adjust your shutter speeds fast enough and you may find you can close down your aperture down for greater depth of field and still get great exposures. That sentence may seem confusing but if you try it yourself you'll find there's no better way to shoot indoor events.


My 24-70 almost never comes off of my crop body. I have the 70-200 2.8 IS and rarely sees the light of day (hey, it's winter, I'm stuck shooting indoors. Can't have a telephoto indoors!). I've covered weddings with this setup and have produced brilliant pictures. When I get my tax return and purchase the 5Dii I'll have even greater ISO performance giving me faster shooting and the ability to stop down even more. Ultimately, it's knowing what kind of conditions/challenges you'll be faced with and what tools you want to get the best results from these situations. I've found that manual settings and high ISO, bracketed flash and an EF 24-70 focal range is the perfect combination that has never let me down.