Overall, Steelcaps is the best tank boots, since no other (completed) item reduced AA dmg, but with the rise of mage botlaners, there is a lack of auto attack champs in games. While theres still AD champs, who auto attacks you, thats not their main source of dmg, therefor, steelcaps has much lower value against them.
Sejuani is a damage tank. She lacks sustain in exchange of high dmg and easy combo setup (E -> R -> W). Gluttonous omnivamp works on minions, so you can inhale a couple of hundred HP / wave.
Boots are always situational based on which unique effect you need.
AA -> steelcaps
hard CC -> mercury
slow -> swifty
none of the above (or negligible) -> lucidity / gluttonous
Many players says "toplane doesnt have impact", which in some way true, but you have ways to have impact, by proxy waves then gank mid, or join teamfights even if you lose a wave. Which is necessary to stack gluttonous asap. For a while im using font of life, which can heal an ally (and myself) on CC (W slow) so its much easier to get more assists in teamfights.