I currently have a nylon one that I like, but just think leather would be better.
Leather sucks up water, stays wet forever, turns green and white, shrinks, and wears the finish on guns.
Other than that, I guess leather is ok.
Some people open their mouth and remove all doubt...
Anyways,
I have used an El Paso Saddlery chest rig for years and it works great. You can use the snap on the bottom and run your belt through or just let it hand naturally, and adjust accordingly. It is a rather comfortable rig.
I also run a Hill People Gear Kit bag but that is built for slightly different purposes.
If you want a simple leather tanker type rig, the EPS tanker is a pretty nice one and rather comfortable. I tend to wear mine over my insulating layers, and under my goretex/waterproof layer.