Be sure to get the right length for your weight.
I've heard from many other snowboarders that generally a lot of experienced snowboarders started with shorter boards (easier to turn, etc), and moved into longer once as they progressed. If you get something around the right size for your weight you should have a good idea of what will work good for you in the future.
Oh- a 158 seems good for your weight, by the way. I'd ride a 157 if I could get away with it, but I'm a bit heavy :P