I've had a mix for have and haven't in the past, and I'll admit that neither types of relationships were exceptionally tragic, in fact most of them have been quite good. But I think it kind of depends on your personality (how accommodating you are) and what kind of mindset you have going into the relationship.
If you go into it thinking, "yeah, it's time to find the girl to settle with, and although she's not quite 'the one', I think we can make it work, I'm getting older anyhow" then yeah, 'settling' is probly not the greatest idea. But if you just like the girl and wanna try things out, why not. Also, it takes a bit of introspection. If you know you're the kinda guy who may suddenly turn asshole and decide that you can't handle the aspects of her you 'settled' with, then you are just being a fool. It's better to man up and accept these things before you hurt anyone.
Having said all that, I'm a happily married man, to a girl who is even *better* than my ideal wife (if that's even possible).