Have used Textra in the past but don't like that you can't send a group message as individual messages (like BCC). Therefore, I have used the stock messaging app since I got my s6 and think it's fine. It's quick, works with multi-tasking, and has reply as individual messages. The bells and whistles are definitely fewer than Textra's.
I am intrigued by Verizon's messaging app that came pre-installed. Apparently, it allows for wifi messaging like iMessages. Has anybody used it? I see it stores only 3 months or so of your text log. Is there any way to back up all messages with something like SMS Backup or is that one of the sacrifices of using Verizon's program? Might give it a try when I travel.