I think exchanging into any of the four beachfront Hilton Head resorts during a summer week is a difficult prospect. Not impossible, but difficult. As an exchanger with a young family I'd be equally happy with Barony Beach, SurfWatch or Grande Ocean and only slightly less happy with Monarch. I place Monarch fourth because it's the oldest and the amenities are not as extensive as at the other three.
All three have indoor and outdoor heated pools and hot tubs, beautifully landscaped grounds, Activity Schedules with so many adult, children and family options that it's impossible to do all of them in one visit, onsite bike rentals and various games (basketball, horseshoes, bean-bag toss, table tennis, etc,) updated interior amenities ... the list goes on.
Barony is the first you come to as you head east on 278, at about mile marker 5. It has six 5-story buildings with all 2BR non-lockoff units. The two gardenside buildings are situated behind the adjacent Westin hotel and the courtyard area between them has recently been refurbished to add the most feature-rich pool of any of the HH Marriotts, a sandy play area, an outdoor kitchen area in a covered pavilion with picnic tables and tv's, and several firepits. The other four buildings are set up with two directly fronting the ocean and two behind those; the units directly facing the ocean are oceanfront while all the rest are oceanside. The new bar/grille that stays open year-round is situated next to the oceanfront pool, another barbecue area sits between the oceanside buildings, and another outdoor "quiet" pool is situated just outside the indoor pool. Exchangers into Barony are more likely to be placed in the gardenside area but you could get lucky.
SurfWatch is the second you'll come across at about mile marker 6. It has five 5-story buildings, all 2BR or 3BR non-lockoff units. The 3BR units are on both ends of all floors in all five buildings with additional 3BR units in the center of the two gardenside buildings. The 2BR units have a King bed in the master with two Queens in the 2nd; the 3BR units have a King in the master with two Queens in each of the 2nd and 3rd. The resort footprint is huge and unlike Barony or Grande Ocean where there are buildings directly adjacent to the ocean, the closest building at SurfWatch is separated from it by a boardwalk over the marsh; it's designated oceanvista. Another boardwalk separates the ov building from the two oceanside buildings, then the two gs buildings are at the entrance to the resort. From the furthest back building it takes a few minutes to walk to the beach but there are golf cart shuttles that run continuously. Resort amenities/activities are very similar to Barony. Of note is that SurfWatch has a newly-designed "movie theatre" in which newer movies are run day and night, many of the activities are centered on environmental concerns, and every unit has a shower in the master that's huge with multiple jets - it's wonderful! Like Barony, exchangers are more likely to be placed into the gardenside units but you might get lucky.
Grande Ocean is just outside the Sea Pines gate and the daily entrance fees to Sea Pines are included with your stay - as pedro47 said the best bike trails are located within Sea Pines. GO has more buildings, ten I believe, all five stories with 2BR non-lockoff units. Most of the units have a King in the master with two Queens in the 2nd but there are a few with a Queen and sleeper sofa in the 2nd. There are only two unit types, oceanfront and oceanside, with the overwhelming majority of oceanfront units being owner-occupied during the highest-demand Plat season. There are multiple pools and hot tubs, with a beachfront bar/grille with the most famous frozen drink bartender on the island. Again the amenities/activities onsite are extensive enough to keep any family happy.
Monarch is last on 278, just inside the gate to Sea Pines with daily admittance fees also included. I'll have to leave the details for an owner to share.
As difficult as it may be to exchange in, I really think that an exchanger can't go wrong with any of them. Good luck!
