I don't know if its my phone or if it's just a resource-heavy app, but I find contacts+ tends to lag a lot or hang and freeze. No such problems with Textra. I also prefer the individual contact notification settings in Textra. Mind you, I haven't tried contacts+ lately. Maybe they've re-written it, so I can't tell you which is better.
All I know is Textra fits my needs. Light, easy on resources, and a few customizations per-contact which is about all I really need in a messaging app