Ryuk can become intangilble, and cannot be killed unless he uses the Death Note to save someone's life that he's attached to, therefore Spawn couldn't ever kill him. I'm sure if Ryuk threatened to kill the people important to him (like the wife and child he left behind), Spawn would surrender pretty quick.
Although Ryuk is probably the only good thing on that show, I think Spawn would shove a bushel of apples up his ass. Spawn has near godlike powers, and Ryuks got what? Some creepy kid with a scrap of paper.
I'm a little surprised this hasn't turned into a flame war.
lol spawn is awesome, but then again all ryuuk has to do is write his name which he can see with his special eyes. once the name is written spawn is dead. ryuuk can only be killed using the book so I guess that is an advantage too. no weapons can hurt him you can't touch him all you can do is see him. and you can only see him once you have touched the book so with that he is at a huge advantage.
yeah the only way to kill him is using the book, but its not as easy as taking it and writing his name. you have to get him to save someone by using the book to protect them. remember how much shit light had to go through just to get the other shinigami just to save misa, which led to him dying.