I was in NYC for the opening series. I had the "wonderful" experience of watching the 20-run outburst by the Yankees... The stadium was very underwhelming, and the outcome (from a Brewers fan perspective) sucked, but the crowd was amazing.
From before the first pitch and throughout the game, they were chanting, cheering, and being generally loud. I LOVED the energy. Music between every pitch, never a lull... the Yankees carry themselves differently.
I wouldn't call them "friendly" or rude, but Yankee fans know who they are - That's for sure. There were maybe a half dozen Brewer fans on the subway, but I was actually surprised by the lack of Brewer fans in the stadium. I was maybe a dozen rows behind the Brewers dugout and saw .... maybe three other Brewers fans. I thought we travelled better.
Overall, I'm glad to have been there (Yankee Stadium), but I really walked away with a greater appreciation for the AmFam experience. We have a great place to watch our team.