The "best" for me was the ARE LS II fiberglass lid. Expensive at $1100 installed, built very solid, not easily removed, no leaks. Not for everyone or their application. I boat alot and carry stuff on a bedslide, perfect for my needs. Hauls a ton of mulch too (in bags of course), some pics:
It was lined and the hardware and shell just seemed better and more heavy duty than some of the others I looked at. Over a year old now (4-07) and still looks brand new. Lots to choose from.