oh how i love these philosophical/meta threads!
i think this partly depends on what you mean by 'best'. Some circumstances demand re-evaluation, as in a new climate or job. Some circumstances offer a great opportunity for style exploration, as Greyscale put it a new social set or increased resources (for example excess time or money or access to exciting boutiques or people who spark your creativity). And so on.
I've found the most illuminating and fruitful style re-evaluations/insights have come when i'm forced to deal with circumstances which made all my typical style strategies completely impractical to downright torturous. (Moving from wonderfully foggy and layering conducive Berkeley thru the tunnel to hothothot Walnut Creek was the biggest one). This type of situation is very hard but can help you strip down to the true essence of your personal style, allowing you to manifest it in more situations than you ever imagined. It's tough, but so freeing and confidence building when you've made it through.
About five years ago i decided to really focus on developing not so much the style i dreamed of, but the closet (and sewing/shopping/structural resources) that would support that style. Of course, my style has developed along the way to working towards this goal but i dont' feel like i've made any drastic changes, nothing where i'm feeling, "OMG i would never have thought i'd have worn this in a million years but i love it!". More like i finally got around to wearing what i wanted to wear but i didn't focus enough on to be able to have that happen everyday. I've had a number of chronic health problems since i was 15 (i'm 52 now), which have prevented me from having a career, finishing college, having children, etc. So i wanted to do something that was a dream growing up instead of simply focusing on everything i can't do. on edit: i see i have some similarities with Janet's motivations here. Hi Janet!
And you have to get dressed anyways Happy Day! steph