I go from as close to normal standing as possible with feet shoulder width apart and one (either or) slightly in front. As i move around they will change so my movements are as balanced as possible. I can't see much point in locking yourself into fighting from one stance for any length of time nor can I see the relevance between your opponents stance and your own. The only thing your opponents stance will relate to is where their attacks are coming from, you should be able to counter everything from the stance you are in. Granted that no-one is completely ambidextrous and there will be things that are more proficient on one side more than the other but would you change your stance for the specific purpose of allowing you do perform a technique? I will tend to do certain techniques from one stance but won't change to go looking for a technique, I'll just do whatever I feel like at the time.