I hear about Elkarte, the released version is much more modern than SMF is. That said, it's still a pretty ancient platform, based on code from the 90s. The only reason it is competitive is because of how bad the competition is.
If you have the money to spare, not just for Xenforo but for some addons, Xenforo is overall the superior platform. Writing add-ons for it is a comparatively wonderful experience, and it certainly isn't losing popularity. IPS, as far as I can tell, is currently better managed overall, however, offering a larger package out of the gate.
I feel if you plan on having something of your own and well free, you need something that you can either integrate into a wider framework easily (SMF/Elkarte) or extend easily (Xenforo).
If you have the money to spare, not just for Xenforo but for some addons, Xenforo is overall the superior platform. Writing add-ons for it is a comparatively wonderful experience, and it certainly isn't losing popularity. IPS, as far as I can tell, is currently better managed overall, however, offering a larger package out of the gate.
I feel if you plan on having something of your own and well free, you need something that you can either integrate into a wider framework easily (SMF/Elkarte) or extend easily (Xenforo).