Do you prefer faster or slower enema solution flow rate?

Definitely slow. A nice warm relaxing enema is something to be savored.

When doing enemas I don't really care how fast or slow it flows into my bowels. I usually hang the enema bag quite high and my enema doesn't last for long time, but I like the pressure of the water in my bowels. I get more pleasure from keeping the enema solution in my stomach and the enema tip in my anus. So I prefer to fill my intestine quickly and then lie down and calmly stroke my belly or masturbate.

If I just want to just quickly fill the lower rectum and release for a quick clean-out, then I don't mind filling fast.

If I want a nice, easy-going, relaxing, soothing enema, then I like a very slow flow. I can hold and retain more.