If Ray Allen was abducted and I had to pick one guy JJ or West to have start in the backcourt with Rondo, I'd take JJ. If Ray Allen is already your starting starting SG with Rondo at PG, I like West better as third guard. He's capable of guarding elite SGs, he can backup either spot, and he's enough of a shooter to fill Ray's role when at off guard. The one thing West cannot do is step in at SF, but he's enough of a defender that you can slide Ray to SF and your team D won't fall off.
I'm not sure TA would even improve the current rotation at the wing/guard spots of Pierce/Allen/Rondo and Daniels/Nate. Would he improve the D over Daniels or Nate? Yes. But the cost offensively probably offsets it.
I'm not surprised TA is on the market, he was a bad signing for that team.