How accurate is good?

I've been looking through a lot of cosplay; for some laughs,and for some "wow" moments. But one thing always crosses my mind.
Wigs.
I've never cosplayed. I'm not dissing it, but is it better to wear a strange coloured shinny wig, or to just try your best dying your hair and getting styled just right? To me, I have to go with the later, but what do cosplayers think?

Thanks for clearing this up in adcance.