As of 29.06.2017, the official spelling rules allow to use the capital eszett (ẞ) and SS when capitalising ß; they do not allow using a lowercase ß (§ 25 E3):
Bei Schreibung mit Großbuchstaben schreibt man SS. Daneben ist auch die Verwendung des Großbuchstabens ẞ möglich. Beispiel: Straße – STRASSE – STRAẞE
Frequency of usage
From my observations, ß is most often capitalised as the lowercase ß (despite this being wrong), considerably less often as SS and even less often as a capital eszett (ẞ). However, the latter is used with surprisingly increasing frequency. This article features some recent uses, including the corporate designs of RWE (a major German electricity company), the SPD (a major German political party), the German football association, and the University of Weimar.
My (hopefully informed) opinion
If it is not a logo or similar: Check if you really want to use all caps, since they decrease legibility, make the text optically disharmonious, and a lot of people feel shouted at by them. Consider using small caps or another type of typographical emphasis (bold, italics, …) instead.
If you can assure that your text is rendered in a font with a proper capital eszett, use it (GOETHESTRAẞE). This is arguably the alternative which least readers will stumble over. I personally used a small-caps eszett before it became official, in a situation with several readers who where supposed to spot mistakes, and nobody noticed. The design of a capital eszett is good, if it cannot be read as a B and if it does not stand out amongst the other capital letters of the font, e.g., by being to narrow (see also here).
Otherwise use SS (GOETHESTRASSE). While this is the preferred variant in the official spelling rules, it is more distracting as readers intuitively read it like a lowercase ss.
Never use a lowercase eszett (GOETHESTRAßE), except for forms where names need to be identified correctly and similar. This is not only officially wrong, but also distracting as the lowercase eszett does not harmonise with the other letters.