I personally use QKSMS, which isn’t perfect, but it’s all I’ve been able to stand since Signal dropped SMS support.
This RCS stuff scares me a bit, because it sounds like it will function over a data connection and not be nearly as universal of a standard as SMS/MMS is. There are already a million such apps and standards if one wants to use data for messaging. Trying to sneak it on top of SMS is very annoying. If I use my SMS app, I want my messages to be sent as such. Getting a surprise data bill shouldn’t be a fear.