Since consistently predictable low crowd times don't really exist at DLR any longer (especially since the 60th anniversary), I'd say your choice depends more on what you'd like to see. Do you want to see HalloweenTime at DLR (a super fun time in the parks)? Your second set of dates will certainly fall during that time and will most likely hit one MHP (probably on the 28th). Your first set of dates falls during Pixar Fest, so if you want to see the Pixar Play Parade in DL, PTN in DCA, and Together Forever fireworks in DL, along with all the special Pixar Fest food and merchandise items, then August it is! Which would you rather see? Both date choices will likely be crowded, but not Christmas week crowded. (HalloweenTime may be a bit more crowded, but that is such a great time at DLR!) So just go with whichever theme appeals to you more.