I vote checkerboard - it breaks up the horizontal line theme of the built-in cabinet. The stripes make for a lot of stripes in the room. Room looks great!
I'd support checkerboard if you had life-sized checkers or chess pieces that you could play with using the carpet as the board. SHort of that, and not sure if that is even possible, i vote for stripes! Also, there is an IKEA in St. Catharines, Canada (in case you didnt know that...) House looks great!