The Obamas stayed at the Bar Harbor Regency. They stayed there because it has a flat roof. Escape could have been made by water, by air, or by road. When the top two suites were booked for the Obamas, the owners totally gutted and redecorated the rooms, right down to regrouting the shower stalls. The Secret Service booked most of the rooms on the floor below.
The Bar Harbor Grand is actually a nicer place than the Regency, although the Regency is on the water and has nice grounds. The Grand is on the southern edge of town and would be in easy walking distance of everything, unlike the Regency.
As for being close to Acadia, most any lodging in Bar Harbor or Southwest Harbor is close to Acadia. The park is spread out over Mount Desert Island which is not all that large an area. Everything is pretty close.
Neither the Grand nor the Regency would be truly upscale. The Bar Harbor Grand, in fact, has the feel of a Hampton Inn. I'd recommend The Bar Harbor Inn or the Harborside Inn or the Bluenose for upscale.
In most opinions three days barely scratches the surface of things to do in Bar Harbor and Acadia. There are no "right trails" to hike. You can stop at the large Acadia National Park Visitors' Center on your way into Bar Harbor. There is a scale model map there and many guides to hiking, walking, kayaking, climbing, and biking. Rangers are on duty to answer your questions.
You will want to drive the Park Loop Road and up to the top of Mount Cadillac when you first get here. That might give you an idea of what area you would like to spend more time in. One good hike is Great Head, on the far side of Sand Beach. It's not too long and not too hard, although not flat and simple either. It has great views out to open ocean. Another hike would be around Jordan Pond, stopping for tea and popovers on the lawn overlooking the pond. The carriage roads are also wonderful for either hiking or biking. Bikes can be rented at several places.