Shall I extract premolar teeth for bracing? If so, first or second premolar? (Photo)

Though most of orthodontists recommended me to extract premolar teeth, I wonder if it is possible to align my teeth and move them a bit backward without extraction. I have removed my lower wisdom teeth. If I must have to extract teeth, which ones I should extract? Different orthodontists give me different proposals. Some recommend #14, #24, #34, #44, some recommend #14,24,35,45. I know usually teeth should be extracted in pairs. Is it ok to extract #4 upper and #5 lower?

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