Messaging App always. I rarely use Skype.
Not a fan of the battery drain that Skype brings when signed in and ready to receive messages.
I just changed the heading to W10M specifically. Does Skype Preview drain battery life on mobile. I haven't used it as DD yet to find out.
Sent from my Lumia 950 on mTalk
Messaging app, tried the Skype and it was okay, but missing some of the functionality of the messaging app, namely the ability to mute messages, I make great use of that and missed it on Skype. Another minor issue was the hide/unhide messages, hiding them was easy enough, but to find them to unhide was not clear or evident that was frustrating as a user experience.
Then there was the issue of Skype not opening, it would just hang and then go back to home screen, yes that was fixed but it didn't offer much for confidence in it as yet.