Never where white straw after labor day or before memorial day, it is just a fashion no no.
I, for one, don't go by that "rule". It just seems a bit silly. I also don't care about fashion. Why are there "rules" regarding the fashion of cowboy hats? Do you really think REAL cowboys/cowgirls care? I don't. If the hat fits and offers protection, wear it regardless. Why should the time of year even matter? If its warm (above 50 or so), I will wear my white straw hat over one of my felts any day. In fact, I wore my white straw yesterday.
I must just have an oddly large head. I wear a 7 1/2.
I like the look of the more expensive felts, but have yet to buy one. Truth be told, if I had one, it wouldn't be worn much because I don't have a reason to wear a nice expensive felt hat. I trail ride and rodeo. Expensive is not easy to replace. My felts are both 4x, which is on the lower end for that reason. As far as straw hats go, if it fits, offers protection, and will last a while, I will wear it. I currently have 4 hats and might be getting a new one soon. I would love to get a custom hat, but they must cost just short of a small fortune.
I have a Resistol white straw that is my work/rodeo hat. I wear it year round if its not too unbearably cold, which is the majority of the year. It just has the stock braided "leather" band. I had a leather band with a horsehair inlay on it until I got a felt that it looked better on. Getting stampede strings for this hat soon.
The second hat is also a Resistol. It is a mexican palm leaf with a horsehair hat band that I purchased at End of the Trail in New Mexico. It is a pretty nice hat for the price. I bought it for $30 at Sheplers in Oklahoma. I wear it mainly in the summer because its not too windy then. This hat seems to blow off of my head easier. It fits, but I still end up chasing it on a windy day. Getting stampede strings for it and my white straw.
The third is a Bailey brown felt. It was bought for about $50 at a local store that has now gone out of business. It was on sale for 75% off, I believe. This hat has a stock band on it, which it braided leather. Don't wear this hat much because it is a pain to clean. It also doesn't fit like a 7 1/2 should. Their sizes seem to run a bit smaller. Might end up giving it to my dad, who wears a 7 3/8, because he likes it and it fits him much better.
Finally, I own a no-name (that I could find- says Amarillo on the inside) black felt hat. I ended up putting the leather hat band with horsehair on this hat. The band is black leather with a white and black horsehair inlay and silver conchos. This hat is so hard to keep clean with all the cats and I dogs we have. However, I do wear this hat more than my other felt. It fits perfectly and is pretty nice for a no-name hat.