Just my $.02, but I wouldn't bother changing hotels just to check out another one. MRG is a modern, comfortable place, a bit off the beaten path, but a great neighborhood to go back to at the end of a long sightseeing day. We stayed there for eight nights last Fall, it's a beautiful quiet street.
The Hilton would be a bit closer to CDG for your last night, not enough to make a difference, really.

As someone posted further up, right out of the hotel is to Glaciere Metro stop; you can also go left, to Denefert-Rochereau station. There is a wonderful patissierie on the left side of Rue Ste Jacque (forget the name, but next to a convenience store, just before Place Denefert-Rochereau.) Opens @ 8AM, IIRC, stop there for jus d'orange, eau, and une croissant chocolat before heading further into Paris.