I have to say I like my BullDog deck. Its a couple years old, but hardly used as it was repo'd from the original purchaser when he bounced a check for the deck. I got a real sweet deal on it. An extension would be handy!!
I have the Truck Boss from Marathon. I'm really happy with it, seals the box so everything stays dry. No plywood to deal with. It is quite a bit heavier than the others out there though. I put the 12" extension on the back of it, as well. The only negative thing I have to say about it, is that it's a bit of a carry on to take it off in the spring.
You definitely get what you pay for, I picked up a Chinese model real cheap couple years ago and it's been fine but easy to see it's built a lot lighter then the expensive ones.
I'm curious if anyone has actually weighed a high end aluminum deck (7' ish) with the ramp compared to an all steel one (with aluminum ramp)? I'd take steel any day for strength - aluminum doesn't like to flex and can crack. My 2 place sled trailer is cracking beside the welds but is also not the heaviest construction. Owning a diesel I'd opt for a little more weight of a steel one next time just for the strength and reliability.