What size snowboard should i buy?

Anything between a 148-153 would be a good size for you based on your height, weight and level of riding.

waht iisa said with the exception that it should be closer to 148 and not 153 because im 5'10" 125lbs and i ride a 153 so just be aware and either try out a friends board or do a demo but demo's cost money while borrowing from a friend doesn't

Check out this site: http://www.burton.com/ProductChooser.aspx It only has burton products on it, but it will give you a pretty good starting point!

it would make sense to get something in the early 150s (150-155). do you mean you do the falling leaf (one foot down hill, stop, other foot down hill, stop, etc.), or that you can use both ways equally (like use you're toe edge and do tricks etc. equally with both), by swithcing from normal to goofy? if you're doing the falling leaf, get like a 150-153, because shorter boards are better for beginners, also get an all round board so you can figure out what you really like to ride. if you can use your toe edge and such equally on both, get a 153-155, because you're advanced enough to have a slightly longer board, and a true twin tip might work well for you, because it wont matter which foot is downhill and its better for tricks