If you are married to an EU citizen (which Brits still are for the time being), then you cannot be denied a visa to accompany him to a different EU country than his home, under the freedom-of-movement directive -- unless the authorities processing the application conclude that the marriage is a sham.
So that's what you should focus on establishing in your visa application. (Once you mention the marriage they will either believe in it or not. In the latter case, your credibility will be shot to pieces in the process, and then your chances of getting the visa on the basis of ordinary tourism are pretty much non-existent anyway).
The refusal you posted in your earlier question shows that the British ECO was not convinced that your marriage is genuine. This doesn't compel the Spanish consulate to reach the same conclusion, of course, but whatever made the UK suspicious in the first place will probably still apply to Spain. Especially if you have never cohabited with your British husband for any significant length of time, you could have a steep climb ahead of you.
We can't give any percentages, though.
(Note that a "genuine" marriage here means more than just having valid legal paperwork. See for example this handbook from the EU for more discussion than you probably thought you wanted about what they consider "genuine").