Default Text messaging apps?

I am considering buying the G Watch or the 360. My concern is the texting app I must use to be able to reply to text messages. I was told I need to use hangouts. I opened hangouts today on my G3 to get used to it and gotta say it kinda sucks. I hate the archive action, lack of customization and it doesn't pull contact photos in for all my people.
Are you able to use other texting apps to get full functionality of Android Wear?
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Device: Galaxy S5