There was an interesting discussion around this a couple of years ago, I was quite surprised to see people still using ESDF: https://news.ycombinator.com/item?id=41148889
My quake 3 bindings where roughly:
Mouse wheel down - Rocket Launcher
Mouse Wheel up - Plasma Gun
Q - Shotgun
W - Lightning Gun
...
This lets you switch directly to the weapon you need without cycling through the weapons in between.