Well it depends on where you live and how many places have scanners. I do believe the scanners can read both types of chips now. I know that my ACO is lazy and forgets all the time to check and we yell at him everytime we get a mad person telling us we should have just checked his chip. We don't have a scanner because they wont give us one for free since the ACO has one. We don't have the money to get one (we are working on that) and the aco wont give us his.
Little things like this make a big difference. If the dog had a tattoo, we would notice that right away. I would do both if you are really really concerned about losing your pet.