I can tell you this much: We always went in Sept. or October, because the crowds were so low. Then, when I started college, and my brother and sister followed, obviously summer or spring break were the only options we had. So we tried spring break - WHAT A NIGHTMARE!!! We were what you call Disney veterans - and navigating those parks was horrendous! Without all of the experience we had, we would've been stuck in 3 hour lines with wall-to-wall people everywhere we turned. DHS was the worst, as it's the smallest, and I remember standing on Hollywood Blvd. feeling claustrophobic on this gorgeous 80 degree day! That being said, however, the weather was gorgeous with only a few rain showers.
Summer, on the other hand, was something we'd always been told to avoid. Crowds AND weather were going to be horrendous, so never do it! Well, we took our big family of 17 in June and while yes, it was hot, it wasn't so terrible, and the crowds were REALLY not that bad! (And remember, I say this when trying to navigate 17 people through the parks.) Then, for the past 3 years, we've gone in August, which, yes is SWELTERING, but if you go towards the end when everyone's back in school BUT the college students, it's awesome! (Tip: If your hair frizzes in the humidity, just remember you won't be taking one decent picture without a ponytail
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So after my rambling explanations, I would never again go during Spring Break, but will be going this summer with my new husband - so excited! Have fun, whatever you decide!