The chip we use in Canada is PetNet:
http://www.petnet.ca/petnet_live/servlet/Index
The nice thing about it, is some municipalities recognize the chip in place of a dog license! :D So you may want to check into what is and is not accepted by your township. You may be able to save money!!
The problem with tattoos is that there isn't a central registry for them. They also tend to blur over time. Tattoos may be for the AKC, CKC, etc. or may be an individual breeders number or code. They're great when you're validating the number of a dog against their paperwork (i.e. for a show or breeding verification), but when you you're trying to identify the individual dog - tattoos fall short.
I adopted a little sheltie years ago from a shelter. She was tattooed, but they had no way to track her owners down. Their loss was my gain!
The chip doesn't degrade, is safe, hurts less than tattoos and is permanent.
It is VERY IMPORTANT to remember to UPDATE YOUR CONTACT INFORMATION IF YOU MOVE!! If your microchip company can't find you - your dog may end up in a high kill shelter with the rest of them. :(