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Ankita SarafAnkita Saraf 

Why most of the future methods are used for callout from trigger, why not batch or queueable apex?

In order to do a callout from trigger, it should be always in asyncronous, It doesn't really matter which operation you are choosing. But while selecting them consider its pros and cons of using it as trigger execution can happen frequently to avoid limits.

1) Queueable methods having advantage over future method having option to get the status of the specific queuable instance triggered over future jobs. You can chain the queuable jobs and maintain the order.
2) But more than one queuable methods cannot be executed parallel in system leads to exception. As you are processing via trigger, there are chances that many user does the DML in parallel lead to exception. More than onre future mehtods are execute in parallel. 
3) Batch jobs cannot be executed more than 5 in parallel leads to run time exception. 

Hope this gives you idea..
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