I'm not sure I have an ideal. I mean, sure, I can pinpoint things I like. But I find the things I dislike to be extremely valuable too.
I've felt terrible at times. Afraid to speak my mind, afraid of hurting others, afraid to be hurt. Yet these are almost always countered by times when I feel like I've made growths by leaps and bounds.
I can't call something "ideal" when there's that much fear floating around, but I couldn't call it ideal without that much growth either.
And.. there's no "an". I'm finding that my relationships feed off of each other and bring up issues that no relationships do by themselves. And none of these issues are the same within different relationships.
For the same reasons why "one isn't enough", I don't think there can be one ideal to me. Every person I care about and relate to brings different things to the table, good and bad, and I don't think of any of them as more or less important, valuable or "ideal".
That... or maybe ALL voluntary relationships are ideal. I dunno.