Hi. For me, it was definitely the fashion of the sixties! (The latter part}, and it wasn't the pillbox hats that I wore, but all the other great clothes of that time. It wasn't called the swinging sixties for no reason! The mini skirt was an icon, the great vibrant colors, the crazy accessories, all made this fashion unique. Everything seemed to blend, the clothes, the music, the whole atmosphere! It was a time when designers made statements with their clothes.Maybe I'm just bias, as I was able to wear these clothes, and experience the freedom of statement. But somehow, I think there was more original ideas in the sixties, than other fashion periods.

My favorite decade of fashion is the 1940’s. The clothing features of the 40s were flattering to the female figure, classic in style, emphasized the waist which produced an "hourglass" silhouette and had shoulder pads in dresses, blouses, shirts and coats to make shoulders square with a military feel. The two piece skirt suit became very popular in the 40's while women enjoyed showing their “real” body contours during that fashion era.
Skirts and dresses were A-line in shape (not pencil tight) and dropped down to the low knee. This was shorter than the 1930's and set the standard for the 50's. And, the two piece swimsuit was invented as well as the Bikini.
Oleg Cassini, Edith Head, Madelaine Vionnet, Dior, Chanel were among the popular designers and stylists during this era.
The overall fashion look included bodices that were fitted with drapery, ruching or gathers with the padded shoulders. The necklines were high and round, sweetheart shaped and had small collars. The shoes were mostly oxfords, pumps and sandals.
Source:
http://www.womeninwwii.com/fashion/1940sfashion.asp
http://www.oldmagazinearticles.com/Fashion_1940s

Keeping in mind that what the fashion designers put forth is not necessarily what everyday people wear, for everyday fashion, I'd have to say either the 40s or the 90s.

In the 40s, we first saw the introduction of a sleek, tailored, yet glamorous look. When you look at old newsreels or photos of crowds, you can see that the women dressed very much the way the people in movies did (unless the movie stars were in evening dress). Couture designers didn't have to resort to budget lines, because the clothing they designed was wearable enough every day that the wealthy actually bought it in great numbers.

In the 90s, there is a similar dynamic at work, although shapes and lines changed. It was now socially accepted by the vast majority for women to wear pants, and most women now worked. Clothing needed to be utilitarian, but with a bit of elegance and sleekness. This time, however, there was a disconnect between the artistic creation of designers and what everyday people actually wore. Designer creations were mostly fanciful and inappropriate for the average person's everyday lives. So there were budget designer lines, but styled more along the average clothing people were wearing.

I would have said the 60s, but I was a child during part of them. People did imitate Jackie Kennedy's look, and that was nice. But in the later 60s, while designer clothing was fun, and what college kids wore was too, the average non-college non-designer-wearing woman had several really gross shades of polyester to choose from: olive drab, burnt orange, sometimes in plaid or bandana print. Or neon paisley. I have old pictures from that era, and my memories, to prove it. Trust me, the 70s were even worse for the average person. It seemed to be a nationwide contest to see who could wear the ugliest clothing!

I vote for the late 60's. It was easier to buy stuff I like then.

http://www.gloriousnoise.com/images/beatles-sgt-pepper-outtake.jpg

When you use the word 'best', I get confused. What would the word 'best' represent in the fashion world for women?

When I think of the 20th century in regards to fashion, I cannot help but focus on the styles of the 20's. The flapper. The revolution that took place through androgynous clothing and hair styles.

From tight fitting corset of the victorian age to nothing at all in such a short time, must have felt so liberating to the typical female. The only comparison we have in our lifetime would be the 60's, but the 20's altering of hem lines and exposure of skin was 10 times as shocking.

Historically speaking, the 20's was the first revolution which changed not only fashion for women but brought them into the forefront to he heard instead of just seen.

This video does a great job of introducing this idea.