I'm a Knick fan who used to live in Brooklyn near the proposed arena. Now I live in NJ, somewhat near the other proposed arena in Newark.
IMO, either proposed arena would be good for the Nets. Obviously, or they wouldn't be trying so hard to relocate. Where they are now is in the swamps. There is just no mojo around there, not to mention train service. If they moved to Newark or Brooklyn they be in a more densly populated urban environment where the community can come by foot, train, bus, or car. Plus there are bars, restaurants, and coffee shops nearby. You could say "lets meet at the corner of 33rd and 3rd, catch the game and then grab a bite". At the Meadowlands you'd say "let's meet in the parking lot under the burned out street lamp, catch the game and then I'll follow you in my car for 30 minutes to ghet a beer, if we don't get lost or in an accident".
Like most large metropolitan areas in the northeast you have affluent areas as well as depressed areas, both in Brooklyn and New Jersey. Some parts of Newark look a lot like parts of Brooklyn. From the little I know of Newark I'd have to say hte affluent neighborhoods of Brooklyn (Brooklyn Heights, Park Slope, etc) exceed Newark's, but I could well be wrong. But Brooklyn's bads may well exceed Newarks bads too. These cities are just plain big enough to have lots of diversity. Sometimes the good neighborhoods are very close to the bad, and it can feel a world apart one or two blocks away. It's cool cause you can go to the nice neighborhoods for the park or the view, and you go to the lesser ones for cheap shopping or "ethnic" food, etc.
But the proposed Brooklyn site is in an interesting area. First, it's a major subway hub. Lot's of lines go there as well as Long Island Transit (a suburban rail line). Second, it's about 1 mile from Manhattan, straight over the Manhattan Bridge. Third, it is a densly populated neighborhood, so fans can walk to the arena. Fourth, there is what constitutes the Brooklyn downtown right there, so you can attract the quasi corporate crowd (not like Manhattan's). Fifth, there are other cultural attractions already nearby, like Juniors restuarant (of cheesecake fame) and the Brooklyn Academy of Music (BAM). It's also close to Fort Greene, of Spike Lee fame, as well as it's art college, the name of which is escaping me. Much more too but my mind is getting lazy.
Anyway, long story short, the Brooklyn site is great because it's been undergoing a renniassance there over the past 10-20 years anyway, but there is still room for improvement. It'd be wonderfully situated. And crosstown rivalries are the BEST.
That said, I'd be equally happy if they'd come to Newark, then I'd even go to a few games.