Difficult question because I'm not sure you can really quantify love like that.
I do believe Spike knew Buffy better. He saw her at her absolute worst and saw her at her most heroic/best and he loved her completely.
Touched:
You listen to me. I've been alive a bit longer than you, and dead a lot longer than that. I've seen things you couldn't imagine, and done things I prefer you didn't. I don't exactly have a reputation for being a thinker. I follow my blood, which doesn't exactly rush in the direction of my brain. So I make a lot of mistakes, a lot of wrong bloody calls. A 100+ years, and there's only one thing I've ever been sure of: you. Hey, look at me. I'm not asking you for anything. When I say, "I love you," it's not because I want you or because I can't have you. It has nothing to do with me. I love what you are, what you do, how you try. I've seen your kindness and your strength. I've seen the best and the worst of you. And I understand with perfect clarity exactly what you are. You're a hell of a woman. You're the one, Buffy.
It continues in the comics (depending on if people take it as canon. I do)
Buffy: He really loves me, Will I can feel it. It's not some storybook pure love, there's fear and lust and doubt about himself, that he doesn't deserve it..an instinct to run, that getting hurt now is better than later. Sometimes I annoy the hell out of him, sometimes he thinks he'd be better off with someone else, or no one. All the things I sometimes feel too but would never say but that's just temporary..fleeting. What stays, what's always there is..love.
For me it doesn't get more complete and beautiful than that