The T480s has so much better build quality. Its all metal vs T480 which is plasticity and soft touch. Not sure why you would choose T480 unless you REALLY need > 24gb ram or giant extended battery.
Even the inside is better built. The plastic front clips of the T480 backplate break super easily, whereas the T480s has replaceable clips.
I have a T480 and I've definitely needed >24GB of ram before when running some VMs. It has come in handy. Don't forget too that the T480 has hot-swappable batteries, which is really nice on extended coding sessions where I'm not plugged in or if I'm traveling. Also, I love the rubbery feel of it. It feels solid in my hand and doesn't slip at all. Admittedly that is subjective though. :-)
Similarly, I can vouch for the T495s' sturdiness. The whole thing genuinely feels like a slab of solid rock (but is still lightweight); I can't quantify how robust this thing is, but Lenovo guarantees that every T495s has been through some sort of military testing where it sits in different environments for several hours (sandstorm, scorching heat, freezing cold, humidity).
Even the inside is better built. The plastic front clips of the T480 backplate break super easily, whereas the T480s has replaceable clips.