If I had a deal from the Brewers that I felt was an 8/10 in terms of return, and a deal from the Yankees that was an 8/10, I'll take the Brewers' package every ****ing day. If I'm going to help my crosstown rival win a trophy, I need to get a premium on my return.
If the Yankees offer me more than the Brewers, I will take the Yankees' offer (assuming it's a notable amount more--if it's just an extra throw-in, **** it). You do what's best for the team. Again though...all things being equal, I will take a non-Yankees offer over a Yankees offer. And although it's been really rare that the Mets would be buying and the Yankees would be selling, I would expect Yankees fans to prefer an equal offer from the Brewers to one from the Mets.