I have seen a lot of people say that the minor second is more dissonant than the tritone. I however don't think of it that way. Don't get me wrong, the minor second is quite dissonant but to put it simply, I think the tritone is the most dissonant interval, not just a very dissonant interval. Part of the reason is that it divides the octave cleanly in half. Now you might think that octave symmetry should make it very consonant. But in fact, this usually turns out not to be the case.
For example, the whole tone scale, as a scale is relatively consonant. But harmonically, it is extremely dissonant. All the fifths are either diminished or augmented. This makes for some weird harmonic progressions. So actually, symmetry is kind of a guarantee for extreme dissonance. That is, unless you consider Dorian to be symmetric(which most don't, when most people say symmetry in music theory, they mean octave symmetry, not palindrome symmetry).
Another reason I view the tritone as being more dissonant has to do with the way it resolves. In a minor second, only 1 note wants to resolve, thus making the minor second want to resolve to a unison. In a tritone, both notes want to resolve into either a third or a sixth via contrary motion. When you build chords based on the tritone, this dissonance is further emphasized. At its most dissonant without extensions, you get 2 tritones with an overlap distance of a minor third or to put it more simply, a diminished seventh chord. This is easily the most dissonant seventh chord that exists and the most urgent to resolve.
Sure, you can delay the resolution of a diminished seventh to build up tension in the piece. A great example of this is the First Movement of Beethoven's Fifth Symphony, where Beethoven repeats the same diminished seventh for more than 2 measures more than once such as here(he does a lot of melodic repeats of the diminished seventh i.e. writes the diminished seventh using the melodic and rhythmic contour of the Fate Motif, but these, even at fortissimo aren't as powerful as the harmonic repeats he does of that same chord i.e using the diminished seventh as a rearticulated suspension):
But the diminished seventh has to resolve, be it to a consonant triad or to a dominant seventh chord. The reason it has to resolve? Those 2 tritones that make up the diminished seventh chord themselves have to resolve. Combining this with its typical harmonic usage as either an extension of dominant function(when it shows up in a major key, it usually is extending an already present dominant function) or as is often used in minor keys, as a substitute for the dominant seventh, leading to a cadence that is pretty much exclusively used in minor, that being vii°7 - i, and it just has to resolve to either the tonic or a dominant seventh. Another common harmonic usage of this chord is to help modulate to distantly related keys, usually minor keys. This again involves resolving the chord to either the new tonic or to a dominant seventh which then resolves to the new tonic.
So, given that the tritone alone has 2 notes that both want to resolve in contrary motion and that the diminished seventh, which is the most dissonant of seventh chords has 2 tritones, is the tritone the most dissonant interval?