One heavy, unscratched, piece of glass.
Real cameras are measured in inches...
AN is Anti-Newton, so you don't get the Newton ring pattern In 30 years of contact printing, I never used AN glass, and never had a problem. It's worth getting heavy glass (I use 1/4-inch thick) to insure good contact. And make sure you have a very flat surface below the glass/negative/photo paper. (I use a second sheet of heavy glass with black 2-ply matt board on top to eliminate reflections.)
"I love my Verito lens, but I always have to sharpen everything in Photoshop..."
You miss 100% of the shots you never take. -- Wayne Gretzky
I have finally settled on a Printfile contact proof printer. Best for the money, IMHO--registration is easy, no danger of finger prints on the glass, it's beautiful! My current safelights are some old GE "Guide Lamp" plug in nite lites which are no longer made (they sold 2 on a card for about a buck at the drug store in the 80's) I also have a short string of red LED Christmas lights bought during the post Christmas close out sales. I use an old enlarger for my light source because I already have one, but a 15 WT in a cheap metal reflector is fine. Add a set of trays, a blotter book, a plastic "Betty Crocker" measuring cup for a graduate, some empty Robitussin syrup bottles (see if your local pharmacist will save them for you) for chemical storage and you're in business.
I steal time at 1/125th of a second, so I don't consider my photography to be Fine Art as much as it is petty larceny.