When choosing a snowboard you also need to consider the positioning of your feet on the board. There are a few holes on the top sheet to give you different placements for your bindings. It’s sometimes just best to experiment with these to see which works best for you. They will often give you the "recommended" stance, so look out for arrows next to the holes. You can also change your stance on the snowboard to accommodate for different riding conditions ie. powder- set your stance back so you have more nose to float above the snow. 
There are 3 types of snowboard with different proportions. These are suited to different types of snowboarding, although its not written in stone and there are many cross over’s.

Directional
This type of board is longer at the front than it is at the back. So it’s certainly designed for going specifically in one direction with your good foot first. This is brilliant for all mountain riding and for carving/ racing/ powder. It’s fast and stable, although it’s not so good for learning switch (snowboarding with your unnatural foot first).

Directional Snowboard

True Twin
Completely even length on the nose and tail. Makes your weight balanced and very easy to maneuver the board. Great for riding switch so many park riders will use this type of board. Not so good for powder riding.

True Twin

Directional Twin
A combination of Directional/ TrueTwin, a good transition snowboard for those taking steps towards a True Twin. Good for all-mountain riding and beginning in the park. Ok at powder too!

Directional Twin

You also need to consider the angles of your feet when you attach your bindings to your snowboard. There are so many variations so just experiment and find one that works for you. A couple of ideas; for a Directional snowboard, have your front foot angled outwards and your back foot straight. For a True Twin, have both feet angled slightly outwards at exactly the same angles, this is called a "Duck Stance" Some people even like their feet just straight forwards, no angles at all.