To me, there is a massive difference between all of those.
It annoys me when people say "ily" because to me, if you cant say the whole word, then you honestly dont mean it and chose not to mean it, which is fine but i think ily is just a waste of writing space.
"I luv you" is pretty much the same. People dont say "i luv you" anymore because it has been taken over by the famous 'ily". "Ily" and "i luv you" are extremely similar and dont really mean anything to anyone.
"I love you" is strong. Those words should only be said when they are meant and are expressed towards a person. You can love family and love friends but im referencing this phrase to relationships. You can have strong feelings for somebody, but is it love or lust? It takes a while to define the two but you just know. But then again, what about love at first sight? You know in yourself how you feel for somebody, and when those feelings are real and arent going away, thats when you know. You as a person just know. And that is when "i love you" should be said. When you feel and mean it. Dont joke around with it.
It comes back to Tams saying "Say what you mean and mean what you say". And how true that saying is. I agree 100% with it. Love it such a beautiful, fun, amazing thing to feel and experience.
"I love you" are strong words, words that mean alot to both sexes.