RAS is the only MREIT that maintained payments on its preferred throughout the downturn. I accumulated a position starting in 2008, trading in and out a number of times. I'm flat now, but that has more to do with investment objectives than the reliability of the yield.
If you are looking for a reliable yield from instruments with limited capital gains potential, any of the RAS preferreds is fine. If you are looking for a dividend that has good potential for appreciation, then you'll probably do better with the common stock of RAS, RSO, NRF, NCT, and perhaps others (those are the mreits I'm currently in.
There are 3 Ras pref issues. You can get details and a link to the prospectus for each in quantumonline.com. All are current on dividends and very unlikely to defer any anytime soon now that RAS common is paying a dividend.
I have traded them from time to time. Currently no position in any of the RAS pref issues and long RAS.