In a redraft league, it really depends on what categories you need. I think this is a fair trade, although 3B is tougher to replace than OF (although both of your options are good). I would try to get a bit more than Stanton first, only b/c Longoria is still a name brand that often carries weight if you tried to move him for a guy like Kemp or Fielder. Might be stretching it, but you never know.
Otherwise, it depends on your categories. If you need steals, then keeping longoria and using Stubbs can be a good move.
Both players represents risk of reinjury, so that factor cancels out. Personally, I would want Longo over Stanton, but it's pretty close.
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