Someone once, very sincerely, said that he understood me, and it was so wonderful a moment I nearly fainted and fell off my chair. (It was platonic and he wasn't trying to get me to shag him)
Up till now, his words have had more impact on me than "I love you" or "I like you"
"I love you" - meh - mothers can love without liking or understanding, and what's the use in that? (For me at least)
"I like you" - it's not too bad I suppose, I'm still deciding if it's better than 'understand', but I doubt it.
I think if you're understood by someone, you'll most likely be liked anyway. In my humble opinion.
So which one of the three do you/would you prefer to hear. You can pick one or you can arrange them in order of importance.
(And I suppose someone will say that they'll want to hear different things depending on whether it's a platonic or romantic relationship - go ahead.)