I have both a Black Stewart and Black Watch from SWK. I tend to wear lighter and brighter colors with the Black Watch because it's dark enough on it's own and I prefer the contrast. I find the Black Stewart a little more versatile so that almost any red, white, green, yellow or black can be worn and still make the kilt stand out. I've even worn it with a blue sportcoat and it looked fine.

Bottom line is what everybody else is saying - pick the one you like best and you'll feel better about it. Just be aware that you didn't even mention accessories yet and that's a whole other ball of fun.