I use MDO mainly. Dibond, aluminum, coroplast, and many others are available at sign supply stores.
Your kinda vague in describing what you'll be doing, indoor, outdoor signage, longevity of the signs your building. All substrates will have better usuage for certain applications and time limits in the weather.
Also, there are many supply stores in Penn., and many members here from Penn. If your more specific with your location, they can probably point you to a supplier right near you.
George