Tattoo ink naturally "migrates" a little bit over the decades, and some people think that tattoos with borders (ie: black outline) will be more discernable over the long run - but there are many other factors that will affect how well it holds up, including but not limited to:
a/ ability of the artist
b/ overall design
c/ how well you take care of it (healing, sun exposure and such)
this is a subject that has been gone over quite a bit. You should be able to find at least a couple of historical threads for perusal.