One is from Verizon and one is from Samsung. If you want to add more download one from Google
Which is better? Personal preference. Personally I like everything Google and hate carriers the most, followed by OEM apps so I use Google messages app. But if you don't care then use the one you like. Probably Samsung messages since it'll integrate well with themes and if you have a Galaxy watch etc.
I've been using Textra. I like that you can set your messages to delay up to 9 seconds after you send them. I've needed to go back a few times and correct my messages a few times.