Depends entirely on the champ and where you're using them.

For pvp, in *almost* all cases you want as much speed as possible, for pve, either you're building for a specific tune speed, or over a certain point it just doesn't make any difference.

For instance, I've been working on my FK hard team recently. Having Croidan the Blue at 340 speed (if i could even reach that, ha!) makes absolutely no difference over having him at 260

Short answer? Yeah everything should have speed. You're at a point in the game where you don't need to waste your time with sub-par items.

The only real exception to that is hyper-specific - for example, I don't use speed on my Stoneskin Lightning Cage teams, because they are built to literally not take damage.