* A handy ability to have at all times, allowing you to "collect" enemy projectiles
* You can actually catch the returned vortex projectiles from an enemy and fire it back (also unlocks an achievement).
* Useful for extended fire fights or for covering your retreats or movement to cover
* Recharges quite quickly for an ability
Overall: A brilliant starting option and if you don't want to use the other two (particle wall due to it's situational usefulness or electric smoke because pilots don't rodeo you) then this is a great choice for the rest of your time in titanfall.
ELECTRIC SMOKE (unlocks at level 13)
* Obscures enemy titan's vision and creates a massive electrical cloud around you
* Damages enemy pilots attached to your titan (killing them if they stay in too long)
* Good for retreating or moving to cover
* Can be used to ambush enemies (combined with the speed of a stryder chassis) by dashing and using a close or mid range weapon
Overall: This can save your life if you are rodeod by enemy pilots and can be used both offensively and defensively. A very handy ability to have on hand. This is the main alternative to take besides the vortex shield.
PARTICLE WALL (unlocks at level 26)
* Best used in bottleneck situations so enemy titans cannot dash to the side and flank your particle wall
* Stops all incoming fire from a single direction
* The wall is relatively small so you need to stay just behind it to prevent splash damage from it's edges
* Situationally useful
Overall: The most situational of the abilities, depending on the the skill of enemies and the chassis types they are using it may be more or less useful. Bottlenecks are your best friend with this ability as you cannot be flanked as you fire at the enemy titans. For general use however you may want to take one of the other abilities.