The webbing-only suspension is heavier, but if you use ring buckles and carabiners, it's much quicker and easier to rig. The rope suspension takes a little bit more time to hang, but it's lighter and less bulky. So it's a question of what's important to you.
As far as the pad slot, I've had mixed success with it - the hammock is so huge on the inside that the pad is able to shift around inside the slot quite a bit. If you don't toss and turn a lot, the pad will pretty much stay underneath you, but if you're a light sleeper like me, who moves around a lot during the night, the pad slot might not work as well.
That said, I still think the double layer is a good idea. It will help the hammock fabric to stretch less, and therefore give you a flatter lay. It's also good to have the option, the pad slot might work a lot better for you than it does for me - I'm using a thick inflatable pad with somewhat slick fabric on the outside. A "stickier", thinner foam mat might stay in place much better.