The aluminum will never break and you will have it forever. I don't like non stick. The stuff can flake off and you have an awful pan. Just plain old aluminum.

Like cilantro, it depends on what I'm making. I like aluminum for cookies and for cakes, although I use 9x13 glass for cakes successfully. I've never seen a round glass cake pan for layer cakes. I use glass for lasagna and meat, but will use glass for casseroles that contain things like noodles. I like glass pie plates.

I also do not care for non-stick, and have discarded the one I had. So, for cookie baking, I'd go for the aluminum. I have one Kaiser brand and like it very much, also a nice Calphalon 9x13 that has held up well.

Annie

Aluminum....hands down. And not that "air bake" stuff....just good old aluminum, the heaviest you can buy...NOT that disposable foil stuff!

Both. You can get a 13 x 9 glass pan at Big Lots, nearly anywhere, cheap, so get whatever is cheapest, it's nice for lasagnas, casseroles, but for bar cookies,

I use a straight edged pan, no rounded corners. Line with parchment.

Trace the bottom on a piece and cut out. Makes removal of cookies sooooo easy.

I've always used glass (Pyrex) because that's what I have. :) It works fine...but it does have the rounded corners. I think a straight sided aluminum pan would be even better.

Thanks everyone. I'm going to get a straight edge aluminum pan and give it a go.

There are a couple more choices:

-Stainless steel, which is more expensive than aluminum (good option if you are concerned with consuming aluminum from pans) - http://www.cutleryandmore.com/american-kitchen/stainless-steel-baking-pan-p120461

-Silicon - which I wouldn't suggest for this size pan.

I would, however, suggest getting both metal and glass (eventually) for all the reasons shared above.

I have an aluminum, straight-sided pan that has a rigid plastic domed lid, which is a nice thing to have, so that's another feature you might like, especially if you need to travel with the pan to a dinner/potluck. I have a stainless steel lasagna pan (so you don't have to be concerned with acidic tomato sauce reacting like it does with aluminum. My glass ones have a wicker basket they sit in for serving.

Once you have your new 13x9" baking dish/pan, you should check your library for cookbooks that are written exclusively for 13x9" bakeware (there are a number of them available). That will give you a good reason to use the baking dish/pan more often. :-) I often make two 13x9" recipes at a time, since they will fit side-by-side in my oven, then freeze one recipe - especially things like bar cookies ;-).

This Taste of Home link has 30 desserts made in a 13x9" pan: http://www.tasteofhome.com/recipes/course/desserts/30-desserts-made-in-a-13-9-pan 

-Grainlady

I make so many bar cookies and casseroles, I have three. One nonstick coated steel one with a plastic cover, one Pyrex glass one with a plastic cover (both of these are great for putting in fridge or transporting and keeping cookies and cakes from drying out) and then I have a cast iron ceramic coated one, barn red outside, white inside, for parties and just all around yumminess. I use the coated steel one the most since it is light. Whatever you get, I highly recommend getting one with a cover.

You have another option. If you don't mind the cookies being a little thinner, you can bake that recipe in your two 8 x 8 pans. A 9 x 13 pan has an area of 117 square inches. The area of two 8 x 8 pans is 128 square inches. Close enough, unless the recipe is a bit scant to begin with.

How about a baking pan conversion charts....plus more information for converting recipes to different pans.

http://dish.allrecipes.com/cake-pan-size-conversions/

http://www.joyofbaking.com/PanSizes.html

You can use the two 8x8s in place of a 9x13. Slight adjustment in time will probably be required. But rather than having to rush out and buy a special pan, you can use what you have.

I don't subscribe to the paranoia over aluminum so I use glass and aluminum. Would like stainless but not in my budget for the little it'd get used here, especially these days. Glass is not easy to clean (I don't have a dishwasher) but is a nice cooking pan and I do use it. I like the airbake type pans (I have non-stick and regular and like them both) for cookies. And these days to ease cleanup I use parchment or foil on pans to save effort.