I've used both styles a lot and as far as I can tell the only real difference is the ease of installation/removal. The scissor type come off and on very easily. Both seem to cut just fine but the scissor type is my choice if it has to go off and on a lot.
I have both but truthfully have only used the newer style to mow so far. I put gator blades on it, and as long as your belts stay tight and you keep your rpm's up and mow at a slow to moderate speed they work pretty well.
Pretty much the same. The lift handles are on opposite sides too. Left on older, right on newer. There was a discussion a while back as to whether the older decks 'float' better too since they are pinned to the front axle.