from a performance point of view, it doesn't make much difference.
actually, any type of tip is going to decrease your performance slightly. in fluid dymanics terms, a tip is what is referred to as a rapid expansion. a rapid expansion occurs any time the diameter of the pipe sharply changes. a pipe open to the air is a type of rapid expansion. you'll always have one of those. by adding a tip, you are essentially making it into two rapid expansions - both of which cause turbulence and resistance to flow. (one where the diameter changes from the pipe diameter to the tip diameter, one where the tip changes to open air)
just thought you might like to know. it's not a big deal, but tips really are only for looks, not helping anything and actually causing a slight decrease in performance.
a tip however can be used to tune the length of the pipe to change resonant frequency or change flow characteristics based on the length of the pipe. in that case, welding would be better as some gas leakage will occur around a clamp on connection.
if you're only doing it for looks, choose what looks better to you. if you want to change it later or remove it to make it easier to clean/shine, get a clamp on.