I know I'm not qualified to answer your question, so if someone else with more working knowledge comments, too, go with their answer. In the meantime, I'll take a stab.

What I've read from others, and agree with, is the STEEM ecosystem is already created, up and running, with social media apps and users. Depending on when EOS finally arrives, STEEM will be a year and a half, two years, or more down the road. So, until there's somewhere to go with EOS other than the promise of a great blockchain with Dan behind it, STEEM is still the only real player up and running.

So, some of this might come down to when SMTs drop vs. EOS, but barring some massive shift to EOS without any major glitches, STEEM wins out because it's already in the space.

In concert with Velocity, I believe the STEEM ecosystem becomes that much more attractive.

I'm not sure how this is all supposed to work, but I also understand that SMTs will allow entrepreneurs to use their own site (existing, modified or new) that can sit independent of the blockchain, and yet still access it with their own token. They won't have to build an app or site from scratch (I believe), or necessarily conform to every protocol or line up with code other than what's necessary to use the SMT.

Those are my guesses. I'm sure there's more, but I hope that gives you something to go on.