It depends on a lot more than the info you have provided. My first step would be to assess the importance of the older one to the team - is he the team's free-kick taker, does he score a lot from them. If he's important then the question is how easy will it be to at least replicate that importance with the new guy. etc etc

Personally (and I'll assume negligible token cost), I'd sell the new guy, since he was a free agent its money for nothing and you'll forget about him easily once the next hotshot (my meaning) comes along.

Such a difficult question tho' - maybe I should just say - the string is this long *holds up arms*