I generally quote my holy trinity: 'Heart of gold, spine of steel, mind like lightning' but well... That's not really accurate. Certainly, intelligence is a must, and being a decent person is the same.
The strength bit is a bit of a odd one since most of the girl's I've loved have been well... hellacious bitches. Certainly towards anyone that tangled with them or theirs, and often towards just about anyone they didn't much care for. But the most recent one (lets call her Jen) is very different. Yes, may the gods have mercy on those who cross her,and she's still a tower of strength to her friends when they need one, but in a very different way to the others. While the others tended to be direct in their methods, Jen works on the assumption that she has no strength (one of the gentlest, nicest girls you'll ever meet) and so achieves similar effects via manipulation, misdirection and misinformation.
I'm not sure where I'm going with this but...