Welcome - Luckily for you someone has done exhaustive reviews of the 28 mm lenses for [particularly] the M8. I urge you to subscribe to Sean Reid's site, where you will be able to learn the subtle differences and benefits of each of the 28s:
http://www.reidreviews.com/reidreviews/
I, and many on this forum, am indebted to Sean. There is no better place to gain the information you are looking for. Go subscribe, you won't regret it.
.................... Chris