I enjoy the sweetness of precum most. Edging him for a long time is the best way to get a lot of that. Taking a long time also seems to open his valves to get more ejaculate when he finally does cum. Take your time and both enjoy, is the most important thing.
I most enjoy a thick load that I can play with in my mouth for a while. Of course I like huge loads. I work hard, so would feel cheated if just one sperm cell gets away or left behind.
...well now I am horny just thinking about it...