The most used SMG at the moment. High fire rate, high damage, long range even for an SMG, fast reload speed and a really cool name, those are the things that makes this gun the most popular SMG to use even until now. These are the top 5 best attachments for the Switchblade X9, this is for a longer range and more control build, although the ADS speed is a bit slower it's still enough to be able to react to enemies that get too close.   

Ranger Foregrip

This attachment improves accuracy a lot, reducing recoil and increasing ADS bullet accuracy at the cost of mobility and ADS speed. This helps a lot for longer range fights.

In-game description: Significantly increases control and accuracy. Ideal for long range combat.

Ups

• -13.8% Vertical recoi -l reduces vertical recoil by a lot, making it easier to hit your shots
• -12.2% ADS Bullet spread - Improves ADS accuracy, making bullets have less spread lessening the chances of missing well aimed shots
• -3.7% Vertical recoil slightly reduces horizontal recoil making it easier to control

Down

• +10% ADS movement speed - slows your movement speed while in ADS 
• +15% ADS time - increases ADS time making it aim slower, but it's not that noticable since the gun's ADS speed is Pretty fast already.

OWC Skeleton Stock

Improves mobility and ADS speed at the cost of stability and accuracy. This attachment is just to balance out the negative effects of the ranger foregrip.

In-game description: Increases mobility but with poor accuracy.

Ups

• +12%ADS Movement speed - increases ADS movement speed, making it easier to move while shooting
• -5% ADS time - slightly decreases ADS time making you aim faster

Downs

• -8% ADS bullet spread - reduces the Accuracy of bullets while in ADS, this isn't really noticable since the ranger foregrip has a bigger increase.
• +8% hit flinch - not a good stat to have since you'll be less accurate when exchanging bullets with enemies
• +3.2% Horizontal recoil - slight increase in recoil
• +3.2% Vertical Recoil - slight increase in recoil

MIP Extended Light Barrel

Another attachment that improves range and accuracy. This one reduces recoil a lot and improves ranged damage which is directly linked to the gun's range in exchange for slower aim time.

In-game description: Extended barrel with slightly increased weight to improve stability and increase firing range. Effective at medium range.

Ups

• -8% ADS Bullet spread - improves ADS bullet accuracy
• +15% Damage range - Improves the range of the gun
• -10% Vertical recoil - lessens recoil making you have an easier time hitting your shots
• -5% Horizontal recoil - slightly lessens horizontal recoil

Downs 

• +12% ADS Time - slows down your aim speed, making it harder to react quickly.

Monolithic Suppressor

This attachment increases range while also making your bullets silent, this is really good so that you can kill enemies at longer distances while also giving them less time to react to where you are because of the silencer.

In-game description: Provides the best noise reduction effect and range with medium weight.

Ups

• Silenced - silencing shots so that you'll be harder to locate 
• +10% damage range - increases range and range of effectiveness of the gun

Downs

• +7% ADS bullet spread - slightly increases the bullets spread while in ADS making you less accurate
• +7% ADS time - slightly increases ADS time making you aim slower

Extended Mag A

Adds 15 more bullets to the mag, this is a must have since the Switchblade X9 has a low bullet count on its base mag.

In-game description: Extended mag with slightly increased weight.

Ups

• +15 magazine capacity - increases magazine capacity giving you more bullets to fire per mag

Downs

• -2% Movement speed - slightly reduces movement speed, this isn't really noticable.
• +10% Sprint-to-fire delay - slows down your aim time after sprinting.

  These are the best attachments for the Switchblade X9, again this build is for more of a ranged and more control build, although you might see a lot of ADS time increase making you have a slower aim time, but those aren't that noticeable since the Switchblade X9 has a pretty fast ADS speed without any attachments.