Loopy is one of the more straightforward planes. Even as a new player there is absolutely never any reason to use Tracker in 4v4. In fact the only time you can somewhat justify using it at all in Altitude is on a wide open map, and even then it usually is not wise. When flying on maps with obstacles, the advanced tracking usually does more harm than good as your missiles will often try to target an enemy plane other than the one you want them to or otherwise quickly turn and crash into something other than an enemy plane.
So if you want to use EMP that leaves Double Fire which has a more powerful but slower tracking attack. In either case you should always use Heavy Armor for your green perk and Turbocharger for your blue perk. Without Heavy Armor it is impossible to stay alive for long as a Loopy. Even with Heavy Armor it doesn’t take much to take you down. Choice of blue perk is less essential (ignoring reverse thrust which you should never use), but you’ll definitely benefit from the faster energy regeneration of Turbocharger more than anything else.
Double Fire is the most commonly used plane in Altitude although it is arguably a little weaker in 4v4 than 6v6. Still, having a plane with EMP or your team or not can significantly affect how the game plays out. Using EMP against defenders is not only easy (defenders have to block the goal), but also very effective. A skilled goalie can make it nearly impossible to score, but it becomes very difficult to block the goal when EMP’d. EMP, when used at the right moment on enemy turrets, can also allow you to grab a ball sitting a bit inside the opposing goal area and quickly shoot it into the goal. Finally EMP is often used to drastically reduce the ability for enemy mirandas to hide behind objects and avoid being killed. However, hitting a skilled Miranda with EMP can be challenging so expect to need a lot of practice before finding much success.
Acid Bomb is a similar projective to EMP, but instead of immobilizing, it briefly drains a little bit of health while making any projectiles that hit that plane cause a little more damage. It is better in some ways in 4v4 and worse in one significant way when compared to 6v6. In 6v6 you simply can hit more planes at once doing more damage because you shooting at a higher number of planes. In 6v6 when a player drops out and it becomes 5v5, I often find the effectiveness of Acid Bomb decreases enough that I switch planes until when/if it becomes 6v6 again. In 4v4 you may not do as much damage, but the damage you cause can be much more important.
Acid can be extremely effective on face offs, perhaps even more so than EMP. If you land an acid bomb right where the ball spawns any opposing plane that picks the ball up or gets close will get hit. There is some difficulty though in that if you don’t get to center fast enough a miranda can grab the ball and get out before the acid hits. If you spawn top you should have no problem on most maps, but sometimes you won’t get there fast enough spawning bottom.
Acid is also very effective in front of the goal. EMP is probably a bit more powerful, but it is a little harder to hit as it doesn’t stick around a little awhile like Acid. Also while EMP can be effective at the goal solo, Acid really needs some teammates firing into the goal area to result in a lot of damage. It can clear the goal very quickly though with some help.
Finally Acid is arguably even more effective at defending against mirandas than EMP in 4v4. EMP is better but only if you have teammates who are good at flanking or otherwise hunting down mirandas / skilled ball carriers in other planes. Often that isn’t the case though and Acid can cause a lot of trouble for mirandas who can be forced into eating the Acid to stay protected behind an object. Even if you aren’t able to kill them they will be down to only a hit or two by the time they are forced out and will be much easier to take down before they can find an open shot.