I have Tablet Talk installed, and really like it. I have never gotten it to connect to my phone via Wifi, but Bluetooth works pretty well. Once in awhile I have to reboot one or both devices when it loses connection (after non-use), but once I do that it works well.
Last night, I also installed MightyText's beta. It's very nice. Being a beta, the downside right now is that it doesn't display contacts, because those aren't stored on the tablet. Unless that's changed, I won't use it long-term, because I haven't memorized the phone # of everyone who texts me! If that is a coming feature, I'll be using it happily. I've used MightyText on my computer for months, and love it.
Both are excellent options for texting from the N7.