To me either way sucks for widening it, i'd rather leave it stock. Mine was widened with the wheels flipped when I bought it and didn't realize how much different it made the quad ride until I got standard offset aftermarket wheels. The steering was so much better and the suspension worked better too, not worth sacrificing for a little extra width that really doesn't help anything.
If you are still set on doing it, flipping the wheels is definitely the safest way, it doesn't add additional points of failure like spacers do. If you use spacers, get the ones that are blocks that bolt to the hub and have their own studs. The stud extenders are sketchy as ****, not worth taking the chance of getting hurt if they break to save a few bucks.