I scored well in the Quantitative and Verbal sections of the GRE when I took it 2 years ago and terribly on the analytical writing section. I took the GRE again 2 weeks ago and my scores on the Quantitative and Verbal sections decreased but there was a sizeable increase in the analytical writing score. Is it a good idea to send both the scores or just the first one? Do universities only consider the best scores or do they average them? I am applying for PhD in Computer Science programs.
The weight of your GRE scores and the extent to which they interpret scores when sent multiple is very dependent upon the university that you are applying to, rather than across programs in the same field. I have seen that some programs provide their stance on multiple scores on their graduate admissions website or departmental website (e.g. welcome multiple scores and will only assess your top scores, have you self-report your highest scores but will nonetheless take into account all score reports received in their admissions process, etc.).
I ran into this same situation, whereby I took the GRE twice and was trying to decide between sending the scores again, being that they were so costly. I reached out to the graduate coordinators at each program I applied to and asked their advice and naturally was given different answers. That being said, if you have the means (read as: money) to send your scores again, I would do it to be safe. Though the analytical writing section may not be the most important section for a PhD in Computer Science, a higher GRE score could potentially impact other facets of your admission, such as the funding you receive.*
*I am not a Computer Science scholar and every program assesses admission and funding differently but provided that funding is such an important component for many of us, I wanted to at least present the idea. Many admissions work on a scale wherein you are assessed holistically, and higher GRE scores could "even out" other components of your application that could be stronger.