Different infections, different mechanisms.
Vampires only need blood, Ghouls need flesh, very fresh flesh, preferably still living fresh.
As I recall, in Book 3, Lilith refers to ghouls as having atrocious table manners.
As to more powerful, well, they are people after all and various people have different strengths.
Both have different "handicaps" if you will.
Vampires, don't like sunlight, but their eating habits are relatively straightforward to maintain. They also like the dirt of their grave for some reason. Unless they are a mana wielder, however, they do not turn into bats or wolves or anything like that. They are extremely hard to kill however.
Ghouls can operate whenever they want, but their eating habits are messier and harder to clean up/hide/cover. They are also a bit tricky to kill, not as hard as a vampire, but still difficult, particularly if they are berserk with hunger.
Generally speaking, most people consider vampires to be more sophisticated and of higher social stature than ghouls; but that really could be the eating habit thing.
The thing is, a newbie vampire is a bit easier to hide than a newbie ghoul; again the eating habits.
An outbreak of ghoulism is generally quite nasty. In many cases they can be mistaken for a zombie outbreak.
Vampirism typically doesn't "break out" because there is the whole formal process of creating new vampires, where as ghoulism transmits very much like a disease.
So, typically, you do not see a lot of very experienced ghouls because they often don't survive long enough, unless protected by someone more senior (like a senior vampire)
That being said, I know of tales of very senior people becoming inflicted with ghoulism. Typically nobility or very rich persons who can hide their eating habits from the general public. These folks are generally the most dangerous of ghouls because if they feed well, you don't know they are ghouls, however, their needs create motivations that make them very dangerous.