Well it used to be. Problem is it's pretty bloated, ads are intrusive, and it's pretty expensive to go premium. I ditched it a while back for chompSMS. Made by the same guys as Textra, but with much more features.
I still use GoSMS, and do not have the intrusive ads that others refer too. In general settings you just turn off Mr. News and Mr. Weather. I like all of the customization and I have no problems with Group or MMS either.