Only poplar leaves tend to squish and suffocate. So just mix them with some other species or break them up a bit.

Fallen leaves are an incredible mulch.

I put boxes around my rosebushes and fill the boxes with leaves (unshredded, as i never shred them). I also use the leaves for mulch over plants that need it, such as oriental lilies. There's a place across the street from the school where i've gotten their bagged leaves for a couple of years, but this year someone came and grabbed them before i did! At least i asked permission - this guy just came and swiped them!

I mulch them and leave them but then I do not have a fancy lawn. Just grass but it's a nice green and in 37 years I have never fertilized. Don't water either . Survival of the fittest and the grass has certainly adapted .

I also use mine to cover my roses, then in the spring I rake them off (mostly) and compost what I can. The rest I put out in clear bags and the city composts them. I find if I leave them in place in the spring, the ground stays frozen a really long time.

I've stopped asking for leaves (tired of the funny looks) and take them from the garbage piles. This year I'm going to take most of them out of the bags and spread them on the garden to break down over winter. On the vegetable patch, I'll dig them in. On other gardens I rake them off in early spring to allow the soil to warm up and then put them back for water retention. Also, I keep some to fill my raised bed/compost piles.