If we're speaking in actual metallurgical terms, the term 'strongest' is a farce right off the bat... Because in modern, real terms, stainless steel is CRAP for any blade over 18" due to chromium making it prone to chipping and breaking... But on short pocket knives and short daggers? It's brilliant, but hard and sometimes toxic to forge dependent on alloy. But that is for a blade.
Using it for armor, stainless is *Generally* superior due to it being lighter, a stronger plate can be made from less metal (i.e. thinner armor just as strong as thicker, thereby even lighter) and corrosion resistant. However, even then, alloys still tip the tables and sway things.
So, to answer realistically, no metal is ever really 'stronger'. Ever. They just have areas of expertise and dominance.
In canon terms, phrik probably wins because it achieves most of the effects of the others while being the most durable at a reasonable weight and density. This is, of course, if you're talking about armor. Weapons, and what KIND of weapon, changes it entirely. This also excludes beskar. Also, there seems to be more to do with the beskar in crushgaunts being micronized letting you catch a lightsaber blade in your hand that it does just being made of beskar on it's own. So who knows who micronized phrik would compare to it as.
*Note: This had been the observations of a real life blade and armorsmith trying to bring logic and metallurgy/science to Star Wars... Please disregard as needed. Do not operate heavy machinery while reading this post. This post may cause drowsiness. This post in banned in California and Puerto Rico.