I actually looked into this a while ago, too. The vast majority of stamps are dull and indistrguishable from each other (way to go, PEs). The only ones with any flavor are as follows: (based on the designs given at
engineer seals):
Alaska - I like the star, and the layout, but not really all that exciting, IMO.
Arkansas - state silhouette
Connecticut - nice, ornate state seal in middle
Louisianna - nice pelican?
Maryland - ornate state seal again
New York - state seal
Pennsylvania - has the keystone theme, but a rather boring, industrial design
Rhode Island - SQAURE (wtf?) and with the state seal - definitely different.
Tennessee - got a bunch of weird, agricultural stuff in it. Kind of messy looking, but different...
Texas - same star as Alaska, but centered more. Boring.
Washington - It's got George Washington's portrait, AND its border is a very engineer-like set of gear teeth. I like this one!
Wyoming - the bucking bronco in the center. Pretty cool!
Of all of those, I'd probably pick Washington as the best, and Wyoming as second coolest. Maybe Louisianna as a third place. I didn't see any of the territories, but trust me that the Pacific territories have bland stamps, unworthy of inclusion in the above list.
I think we, as engineers of the 21st century, owe it to our professions to get ourselves into positions of power some day so we can change our state engineering seals to more interesting designs.