Ranger is there most versatile of all 4 javs. It can also do the highest combo damage, but only to single targets. Ranger also has some of the best javelin specific components, which can increase offensive and defensive capabilities.
Colossus can do area of effect attacks, usually called blast damage. Its combo can be performed on multiple targets at once. It has the most armor of all the javelins, so you can tank like there is no tomorrow.
Storm has all type of elemental attacks and can Hover for a long duration. While hovering, its Shields are amplified, so the damage received is reduced. Storm combos are chains, which means when a combo is performed, the status effect of the primer is applied to nearby targets.
Interceptor relies on close range melee type attacks, which can be chained with its melee weapon. It has the least armor, but it very fast. When it performs a combo, it gains the aura of the primer. What aura does is it does damage over time within a radius to nearby enemies.