We love both. Both have relaxed atmospheres. Both have GREAT CMs and plentiful activities for children and young teens.
I prefer HHI for birdwatching and general wildlife encounters. The marshes and intercoastal waterway really brings the wildlife to you. VB has plenty of wildlife, but mainly at a distance.
The beaches are different. HHI has very shallow and long beach shelf and waves are zero to minimal, whereas VB has a deeper and shorter shelf and produces 2' to 6' waves. The other major difference is the VB resort sits right on the beach, whereas the HHI resort sits on the marsh and has a beach-house fronting the ocean about 1.5 miles away.
HH Island and the beach (not the
DVC resort) can be VERY crowded in peak season (mid June - mid Sept). You can walk out onto the beach from the DVC beach-house to find thousands of people there. AT VB over a 100 people would unusual.
HHI has grocery and other stores much closer and within easy biking distance. They also seem to have a better scheme for biking paths. VB has a path, but it is one 8 mile path up to Pelican Island. HHI is much more spread out than VB and I find it much more enjoyable to have bikes even for going to and from the pool (we stay in the lodge). VB is pretty compact and everything is within a 2 minute walk.
HHI has a main resort pool and the beach-house pool, but both seem undersized to me. I think VB has the better slide.
Lately, we tend to alternate from VB to HHI and then BWV once about every 3 years. As I said we love both and I think you need to visit both at some time to get your own feel for them.
If you have infant(s) or toddler(s) I would say go to VB. Everything, the room, pool, beach, mini-golf, restaurants are a 2 minute walk. Emergency visits back to the room are quick and easy. Also, they have a zero depth water play area that is fully contained with one entrance/exit.
HHI has an abundance of restaurants and shopping nearby. If you are not the cook-at-home while on vacation types then you might get tired real quick with the VB selection of restaurants.
That is just some of the differences and likenesses.