We wouldn't worry about staying at the Maldron Parnell Square. It's popular with visitors on these forums, including a number of lone women travellers, and no-one has reported any difficulties. One of us worked just across from the Maldron for a number of years without any problems but the area does look grittier than Merrion Square and marks the edge of 'tourist' Dublin.
But Merrion Square is a much nicer area and is closer to a lot of the action (popular sights and attractions, the best restaurants, traditional pubs, etc.) and is only about 5 minutes' walk from Westland Row DART (Dublin Area Rapid Transit) out of the city centre to coastal locations such as Howth, Malahide, Dalkey etc. It is also likely to be a bit quieter than other city centre locations at night.
Of the three Merrion Square O'Callaghan Hotels, the Davenport and Alexander are four star while the Mont Clare is three star. The Mont Clare is an old Dublin landmark and has smaller, more traditional rooms while the other two hotels are new builds with bigger, more modern rooms and facilities. Between the Alexander and the Davenport, for us the Davenport has more character as it,s built behind the restored facade of a 19th century Plymouth Brethern meeting house. The Gingerman Pub, which is adjacent to both hotels, is one of Dublin's nicest.
Edited: 26 October 2010, 10:42