Aside from the numbers game, ICBMs used to be the fastest way to deliver a warhead, with the obvious drawback that anyone watching the horizon can see it coming from half a world away.
Nuclear warheads have been further miniaturized since the cold war, it is now possible to fit them into cruise missiles.
> The deployment of Kalibr missiles, long-range, low-flying, capable of carrying conventional or nuclear warheads, available in land-attack, anti-ship and anti-submarine variants, was said to have altered the military balance in Europe and potentially compromised the NATO missile defence system under construction in Europe. [0]
There's also the rumored/propagandized hypersonic, nuclear powered cruise missiles (skyfall [1]) that are meant to defeat missile defense and circumvent MAD by enabling undetected first strike.
[0] https://en.m.wikipedia.org/wiki/Submarine-launched_cruise_mi...
[1] https://en.m.wikipedia.org/wiki/9M730_Burevestnik
Disclaimer, I'm just a web developer with access to wikipedia yo