SPIKE: He was good for her in so many ways, especially S6 (yes I know this is controversial!) and definitely in S7. The Slayer is complex, and her surround of family + friends often unintentionally made her feel alien, self-doubting, and guilty at her authentic feelings. Spike provided her with a space for refuge and self-discovery, even if it was initially painful and confusing. It eventually made her a more balanced, stronger Slayer, capable of accepting her own capacity for darkness, and realising that it was OK to have that side and it made her no less worthy of love. Spike was a catalyst to bring out strength and clarity in Buffy. To give a buddhist example: a glass with dirt sitting at the bottom layer looks clean and transparent when still, but when stirred, causes the mud to rise and come to surface. Spike helped her see herself with more clarity and rise above her own inner fears, and she was a similar catalyst for him, making him see his own monstrousness to propel him to change, and he ended up with a soul. Spike and Buffy were the opposite of delusional love. They skirted it, yes, but were ultimately forced to unflinchingly see themselves in a mirror and improve on themselves. They loved each other for their authentic selves, not idealised versions. Buffy's issues of guilt/ self loathing mirrored Spike's angst in dealing with feelings opposite to his calling ("there's a traitor here beneath my breast", "I touch the fire and it freezes me"). She felt like a fraud Slayer often, feeling like nobody could love her true self, that she could only be accepted if she fell in line with the "norm". The love she got from from family/friends was expansive, but conditional to an extent. (Her fight with Joyce had her leave home, Giles, Dawn and even Willow mutinied in Empty Places, Giles left at a time she really needed him, etc.) With Spike, it was unconditional, which was good for her.
WILLOW: Willow literally brought her back from the dead! That's a big deal. Willow was a relentless ally and an incredibly supportive friend through thick and thin. They grew through life's challenges together, which was so good for her. Willow was close to being as powerful as Buffy, which helped them bond sometimes in mutual understanding of inner struggles. Neither was ever consciously judgmental of the other. It was beautiful to watch their friendship. I loved how protective Willow was of Buffy too, emotionally and otherwise.
Giles: An indispensable, loving (and lovable) father figure. My favourite moment between them (and which surprised me) is when Buffy, squirming and ashamed, relates to him how money is tight, she's been sleeping with Spike, and Dawn's "gone klepto", simply burst out laughing, till she cracks up with him at the absurd comicality of it all. No judgement. It was a beautiful moment. Giles has always been an incredible figure of support and anchoring.
Dawn: Dawn was a bit of a whiner, yes, and at times proved a lot for Buffy to take responsibility for, but Dawn utterly loved Buffy. She depended on her but she also hero-worshipped her, and was fiercely protective of her. I think she was good for Buffy in all those respects.
Tara: This might seem an unusual choice, but Tara was wonderful for Buffy. She was a somewhat new addition to the Scoobies, so she could function as an objective outsider, but was also close enough to trust. She had remarkable maturity, insight, and sensitivity when talking to Buffy. Tara was the only one to be immediately understanding and accepting when Buffy hated herself in 'Dead Things', crying that there was something wrong with her. She accepted her free of judgement, and free of conditions, telling her it wasn't unhealthy for her to be with Spike. When Joyce died, Tara was also a support, offering to talk to her from her own experience, should Buffy feel the need.
Joyce: Her loving, fiercely protective, and understanding mom. She anchored and grounded Buffy in untold ways, and was a wellspring of love and support.
Angel: Putting their romantic angle aside, Angel was a great ally, and came by to fight by her side at crucial points.
Riley (sort of): Yes, I'm putting Riley in, but with a HUGE caveat: I think he was in equal parts terrible for her but also good for her. He had some redeeming features in the ways he was good for her - I think he genuinely tried his best to be a great boyfriend for Buffy. He was (for the most part) stable, supportive, loving, I liked his final stand against the robotic military reductionism of the Initiative. I liked how romantic he was with her in the beginning, I love that he provided some stable strength when at her side. I love how he let it slip that she was "still quite the hottie" in As You Were- he might have simply thought it but not said it (considering she dumped him.) I love the little bit of wisdom he imparted to Buffy: "wheel's always turning, Buffy." I loved the way he gingerly tried to flirt with her at the beginning, it was touching and it was also great the way he tried to swallow some of his insecurity to hold it through until the crisis with Buffy's mom dissipated. I could tell Buffy honestly felt happy at having a "stable" boyfriend finally (or so she thought.) But there were countless ways in which he was absolutely TERRIBLE for her and actually contributed to her self-destruction to some extent, so that's why this comes last.
