What is the resolution to make images for the api application?

Question

Mobile development

Hello !
I'm studying application development and I have a question. At the moment I'm studying getting data via api for the application.
What is the best resolution to prepare an image for loading it into the application using api so that it does not load for a long time and the quality is not bad, the image is planned for the entire screen width.
Is there a sweet spot between image quality and optimal download speed?
Or load different images for different devices?
Of course, I understand that it is better to make up on mobile devices in dp and about @2x @3x xxhdp, etc. ... But still, the image received from the external server has a resolution in pixels.
Thanks in advance !

Answer 1

250-500kb, jpg, quality 7/10