I like seiza because it's so familiar and it keeps my back straight.
Whatever position you choose, it will become uncomfortable if you stay in it for long enough. This is usually considered a 'distraction' much like the wandering mind. That is, you my find it useful, whenever you notice that your mind has moved over to the discomfort, to simply gently escort it back to the breathing (or whatever). This will, of course, be difficult. On the other hand, it was also difficult to stop the mind from wandering. Meditation can be a challenging experience if you want it to be.
I really liked Kev Price's comments about just sitting.