Hi Rogelio,
Agreed, the Real-Time Preview functionality is in need of a complete redesign and reimplementation. This is probably one of the first things I should attack after the current high-priority tasks: improved astrometry support, new mosaic generation tool, new version of DBE, new JavaScript engine based on Google's V8. Hopefully a new R-T preview, at least with some basic improvements, will be available this year.
As for the default smooth mode, well, IMO it is the best option in most cases. I'll include a new permanent setting to remember the user's selection across application executions. Thanks for pointing all of this stuff out.