I've stayed at both. In terms of distance to the theme parks, they really are equivalent. Travel times courtesy of Bing Maps:
Hilton Bonnet Creek
- To Magic Kingdom Toll Plaza: 5.0 miles or 10 minutes
- To Epcot Toll Plaza: 4.5 miles or 10 minutes
- To Disney Studios Toll Plaza: 2.5 miles or 7 minutes
- To Disney's Animal Kingdom Toll Plaza: 5.5 miles or 11 minutes
Hilton Lake Buena Vista
- To Magic Kingdom Toll Plaza: 5.2 miles or 10 minutes
- To Epcot Toll Plaza: 6.1 miles or 10 minutes
- To Disney Studios Toll Plaza: 3.2 miles or 7 minutes
- To Disney's Animal Kingdom Toll Plaza: 6.2 miles or 11 minutes
A couple of things. There are four Hilton-branded properties located at Disney World. (Technically, the Hilton Bonnet Creek is off-site. But, the access roads are inside Disney so it feels like it's on-site.) There are three adjacent to Disney Springs: Hilton Lake Buena Vista, Hilton Buena Vista Palace, and DoubleTree Suites.
Of the four, the Hilton Lake Buena Vista is the least desirable. It's decidedly average and in desperate need of a full renovation and staff retraining. (This opinion is based on 40+ nights over the past few years.) I would never consider spending the 50,000 points/night that they ask for that hotel.
The Hilton Buena Vista Palace completely renovated their public areas, including adding a lazy river. Their guest rooms really need a makeover and a thorough cleaning. Although, I think they are in the process of refreshing the rooms.
The DoubleTree Suites is my favorite area hotel. All accommodations are two-room suites that were renovated a few years ago. The staff is friendly and seems to care about guests. I've stayed there about 60+ nights in the past few years.
The Hilton Bonnet Creek is a newer hotel with very nice amenities. It is a convention hotel, so there's a good chance you'll see people in business attire wearing nametags. I stayed there once but ended up switching to the DoubleTree Suites after one night because the convention group was out-of-control noisy. (Who knew accountants would be so wild?) The staff was responsive to my concerns about the group. I'd probably have returned, but the DoubleTree folks treat me so well.
Long story short: For a points redemption between your two choices, I'd go for Bonnet Creek without a second though.