I'm not convinced that he is healthy. Assuming that, I'd have to put Boldin ahead of him. Now, if both were healthy I'd agree with you.
Also, assuming he's even healthy, would he really be an upgrade over any Urschel/Jensen/Gusa? I'd love to have some protection for Joe, too, but at this stage of his career would he help our QB sleep well at night?
On the other hand we have an old WR but with the skill that our current unit lacks. If the price is right (not more than 2/2.5 a year) I'd consider it. Unless we employ a ton of 2TE formations we still miss a reliable wideout.
I can't even blame the draft for the situation, cause except for a few slot guys, plus Williams and Davis, the depth was embarassing.
I wouldn't be mad at either move, but Mangold has a very big question mark pending. I'd spend those money on the more 'secure' investment.