Just to avoid unnecessary confusion. sometimes, border officers are stupid and do not tolerant any flexibility.
For example, if you apply under 'Compute system Analyst', make your employment letter title to be computer system analyst and job description matches this title in OOH or O'net. Same if you apply under Software Engineer, make your employment letter to have same title and description as software engineer. As to which category to apply, it depends on your degree. If your degree is computer science, computer system analyst might be better. If your degree is engineering, software engineer might be better, cause I have a degree in computer science, and was questioned by a border officer saying I must have an engineering degree or software engineering to apply for Software Engineer.
For example, if you apply under 'Compute system Analyst', make your employment letter title to be computer system analyst and job description matches this title in OOH or O'net. Same if you apply under Software Engineer, make your employment letter to have same title and description as software engineer. As to which category to apply, it depends on your degree. If your degree is computer science, computer system analyst might be better. If your degree is engineering, software engineer might be better, cause I have a degree in computer science, and was questioned by a border officer saying I must have an engineering degree or software engineering to apply for Software Engineer.