"What's the "highlights" of each and the overall "feel"?"
Generally, when I am at VB, I "feel" as relaxed as I do as when I am on a cruise... You can close your eyes and feel the ocean breezes.. Palm trees and tropical flora surround you. Buildings are themed in more relaxed tones. There are poolside massages, etc...
At HHI, I reminice back to the days when I was a kid and went to summer camp... The resort has places to play horse shoes and hammocks all over. Buildings are randomly placed to give you the impression that you are at a hunting/fishing camp. You endlessly search for Shadow, hoping to catch a glipse, and if you are fortunate, some 8 year old may be "crabbing" out on the boardwalk. The ocean is a bit further away, but the sound of the bullfrogs at night makes up for it.
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"I will have a 6yo and an almost 3yo at the time. Don't know much about either resort."
I have a 6yo and 3yo as well... Both kids love both resorts... Both have a ton of activities for the kids, and IMO have the best CM's out of any Disney resorts. HHI's activities tend to be more nature based. My kids love the offsite resorts just as much as the WDW ones...
As a parent, VB may be slightly more managable only because it is smaller. Pretty much everything is centered around the pool/Inn area and is within walking distance. At HHI, things are a bit more spread out, and if you want to go to the beach or Signals pool, you need to drive or take the resort shuttle.
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"How about month? Is there big differences in June vs. July vs. August?"
HHI tends to run about 5-10 degrees F cooler than VB, but any of those months should be warm... While both are in hurricane zones, I would probabily hesitate a bit before booking an August VB trip. (I only say this because it got clobbered a few years ago by hurricanes Francis and Jeannene. The resort was closed for a few weeks while everything was repaired. That being said, I went back in August 2005 with no problems.)
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"Is it worthwhile to get a 1 bedroom for the kitchen and just go grocery shopping? Will the point difference ($'s) be best used in the kitchen considering the $$ we'll save on eating out if we just used our kitchen?"
This really depends on how much you plan on leaving the resort property... HHI has several fine restaurants within walking distance, but only counter service onsite. If you don't mind taking the kids offsite when its time to eat, then Studio room can work..
VB has three onsite restaurants plus counter service. Since the resort is smaller, its not usually a hassle to get the kids and go out and eat... There are several restaurants nearby, but you will have to drive to get to any of them.
Personally, I get the 1BRs when I go to either... Breakfasts are so much easier when no one has to rush while getting dressed...