+2 speed top tier. Early game AS is a pain. 2 AS is huge value: more bulk, more damage, and allows heavier weapons (training -> iron sooner). Going myrm also gives +1 speed, which pushes AS immediately, and increases speed growth (only 5, but it's there). Arguably, +1 spd class change is more valuable due to a free 1 AS at lvl 5, but +2 speed keeps the AS train rolling.
E.G. Dimitri has decent spd base/growth, but will be doubled. Put AS on him for more bulk and damage -> he fights more often getting him more exp -> he gets even more due to his personal -> Dimitri snowballs.
TL;DR: +2 speed is better than other +2s because AS and myrm best beginner class. Over valuing late game is a trap.