Flatland, Dirt, Street? Ive heard good things about the Free Agent Hellcat and the DK Cinncinati, but I dont go by what other people say. I ride the M6 for flatland and the Haro F3 and F4 for everything else. I also have a custom built bike that I use for street ONLY.
Bike shops have some completes that are likely over priced and quite often the shop knows very little about freestyle and won't just give you the wrong bike, they will actually justify components that are not correct for freestyle bmx. Be very wary of bike shops. Ask around, get information from experienced riders, check www.bmxtest.com and don't just go buy something because you have $300.00 burning a hole in your pocket.
The DK Cincinnati is the way to go if you are just looking to do some random riding and have a good time. Inexpensive and good design. Don't expect it to last forever, especially if you aren't familiar with bike maintenance.
I kind of think the 'first' bike should be less expensive because as stuff comes loose it will break. No matter how muh a bike costs, if stuff comes loose, it will break. So, would you rather see your $600.00 bike fall apart because you are just figuring out how to work on it, or would you rather see your $200.00 bike come apart?
You can make a $200.00 bike last for several years if you know how to take care of everything, or if you at least try hard and work on the bike immediately as stuff comes loose.