I'd rather get Werth, to be honest. More of a complete player.
Not even close. Werth would be a big plus, but Crawford is the better player. Crawford is a very good defensive LF, a great baserunner, shows tons of plate discipline and hits for good power in the best division in baseball.
Werth is about even with the bat with an advantage in HRs. He's a very good defensive RF and a good baserunner. I think RF is a bigger need for the Nats, Werth will definitely be the cheaper option, and he would immediately weaken our biggest division rival.
Final difference is that Werth turns 32 next May while Crawford will be 30 next August.