At this point in time I would go for a twitter type app and something like safepress.
For twitter-ish apps, knowing that there are options that can potentially have less or no ads, never mess with your personal info and are not curated or edited or selectively removed could be a big draw
For safepress, for me anyway, knowing my data is safe, my uptime is theoretically 100% and I can post whatever comes into my twisted head is a big plus. Also the option of having opt IN filters and white/black lists is a huge draw, and that the more popular my site becomes the faster it runs will be some potentially big marketing points.
As for UI, the front ends have gotten pretty back-end agnostic as far as having options like Boostrap and all the new frameworks for HTML5, Electron, PhoneGap, etc. keeps the cost of the UI development fairly low…
there is just so much dang potential it is hard to narrow it down though!!! Can you imagine something like SharePoint or Salesforce on the business side being on SAFE??!! epic!