Well, I used both apps for so long on my Samsung Galaxy S5 and to be honest, the results surprise me. First of all, Hangouts is a great message app. You have so many options and settings, but is it worth the 150-200 MB RAM that it requires to run almost every time? Depends. If you’re really into Hangouts, then you should probably go for it, but if you’re using it just for SMS, well the game changes a bit. It’s kind of laggy sometimes and I don’t see the real point of using it. Yes, it sends messages a bit faster than the message app designed by Samsung, but you’ll run a 200MB RAM app just for that one second? Personally, no.
On the other hand, the message app designed by Samsung is not that laggy and you’ll still get tons of options. Also, it requires only 100MB RAM to run it and sometimes, even less. I used this app while chatting with three friends and it was eating only 70MB RAM. So, if we do the math, Hangouts is not an app that you should use when you care about free RAM space. In my oppinion, if you want to have more free RAM space and the same amount of settings like Hangouts, you should definitely use the stock message app. If you use Google Plus that much (yeah, sure) and you want do video calls with your G+ friends, then you should go for Google Hangouts. By the way, video call quality is just plain rubbish. I tried with a friend of mine and it was even slower than Skype.
Let me know in the comments section below what message application you use. Hangouts or stock message app?