@HollyP unfortunately both places feature slabs Especially on the easier grades.
Summary: Chamonix climbing almost exclusively requires a lift, with the exception of a couple of crags you can drive&walk to. Ailefroide more easy multipitches at an easy reach. Chamoix has lots of exciting granite crack climbing and alpine routes at faster reach with the lifts.
Ailefroide itself is granite but starting from 20min drive down the valley there are top quality limestone sports crags of which many are north facing, so ideal in the summer heat. The Briancon area has a huge variety of amazing limestole crags, grades ranging the full spectrum. Steeper easy stuff has plenty of holds, slabby easy stuff is still more feasible than Bregaglia granite slabs For those interested in hard sport stuff after or before the alpine week, Ceuse is only a few hours drive away from Ailefroide. And it IS the best crag in the world, without a question, if you climb F6c upwards!
Chamonix is amazing if you want to have quick access to high mountain, you save one full day of walking so your legs are happier and you can do more in a week. However, it is not great for anyone who wants to climb harder sports routes or who has no budget to take the lift everyday. Big contrast to Ailefroid is that you need to drive around (or try to move around with the local train) if you want to find the easier climbing in the valley. I love Chamonix, it used to be my home for 5 years, I still go multiple times every year and I have done some of my best alpine days out there. However it is very crowded and pricey.
I think honestly that Ailefroide is better for a big group as the climbing grades start from very low. As a bonus the campsite is a cute alpine forest/field where you can do what you want, including light a campfire.
I am planning to be visiting both this summer, so very happy with either!