How long is a piece of string?
Cat5e STP will cost less that Cat6, so the former is "better" when considering the cost.
Cat5e STP is more flexible that Cat6, so the latter is "better" when considering rigidity.
Cat5e STP has a smaller minimum bending radius than Cat6, so the former is "better" if the cable has to be run through a restricted infrastructure.
Cat5e STP is somewhat more difficult to obtain, so Cat6 is "better" when considering the source of supply.
And so on . . .
Cat5e UTP (the most common form), Cat5e STP or Cat6? It really depends upon circumstance.