I've done July 4th and Spring Break timing before, back at least 14 yrs ago. Since those were so long ago, I won't include them in my commentary, other than to say they were both VERY crowded (and July 4th was crowded AND stinkin' hot!)
We did the week of (and including) Xmas back in '98. Frankly, the crowds were quite low every day... we were amazed! THen came Christmas morning... we went to mass and then to MK and I swear -- it was like every human on earth had stormed the Disney gates and somehow gotten in! Of course, we didn't get to experiece it for very long, anyway, as on this day, over half our party came down with stomach flu (and the other half was left to tend them in the villa!)
In 99 we went during Columbus Day week (not too bad -- but it was rainy and chilly, which may have suppressed the crowds!) Even we weren't too keen on doing the parks... which is how we came to end up at the
DVC office at BW signing on the dotted line!
In 2001 we tried New Years and the week that followed it. For every day past New Years, the parks got better and better! The decorations of xmas were still up, too (although, for some reason, it's just NOT the same as seeing the decorations BEFORE Christmas... Used decor doesn't cut it... I'm such a particularist.) We really loved the easy pase of this time of year -- but the weather was chilly. Mind you, we had 70 and 80 degree weather on that xmas week trip -- but it was a Florida freakish 40s and 50s for this week -- a few days it may have hit high 50s in the direct sun! THe kids and DH prefer Florida when it's warm enough to swim.
Frankly, we rather like our late August timing now. Hot enough to swim, but lower crowds due to southern school calendars. I suppose that late Sept or Nov might be nice, but those will have to wait until our kids are out of school!