I like Werners. For my bigger ladders, I go fiberglass, I feel it has less flex, and in the bigger, higher duty ratings, the weight is negligible. A 40' ladder is a 2 person job either way. The only problem with the fiberglass is you are not supposed to use the clamp style stabilizers. Werner makes a "quick lock" stabilizer for their ladders, it works good. I also like the walk through ladder top rails for getting on and off roofs.

We rarely use our 40' ladder. It is aluminum. I think I got it on craigslist from a contractor. They are stiffer even when extended compared to the 24' extended.

Note that on some of the longer lengths of ladders Werner makes a version that is a little wider, and a standard width in the same duty rating. Get the wider one. I think it's only an inch but it helps. The wider one also feels stiffer to me. Look on Werner's website and find the corresponding model number when buying from whatever store. I had to order my from Home Depot to get the right one.

I use all aluminum for my "normal" ladders. I keep a 28' extension and a 10' step on the truck at all times, both aluminum. In the smaller sizes the aluminum versions are much lighter, especially the step ladder. I use the 32' or 40' fiberglass when needed. Like Tim says, I use the 40' very little, but the 32" comes in handy quite often.

Another really nice thing to have for your personal or sales vehicle is a telescopic ladder. I did not want to put a ladder rack on my sales vehicle, which for now is still my personal truck. I bought a 250lb rated Xtend ladder from Sherwin Williams, and it is AWESOME!