While this is an interesting discussion topic, I agree that getting one over another because /. tells you that something is cool is actually not cool at all, and to do so actually shows that you are maybe not ready for tattoos. If it's not really meaningful to you, don't get it.
That said, you can safely ignore the douche brigade telling you that tattoos are "lame" and "forever". Getting a picture of a skull with a pair of crossed machine guns under it with a Confederate flag in the background is one thing, being a math nerd and getting some equations inked is quite another.
My advice would be to go with the ones you know you want and leave some space available for later equations. You can always go get more ink, and you will probably come up with a lot of additional ideas once you have a couple of the equations inked.