I really liked Mankiw, excellently structured I thought. Never used Begg, it was on the reading list, but I never used it.
As has been mentioned on the ARAM thread, Ruane will be leaving Trinity, so don't choose subjects based on her being the lecturer. This year that advice applies more than usual. There are a good deal of changes in staff on the way, and almost all economics courses are liable to be shaken up somewhat. Make sure to select the course that seems most interesting to you, not the one that has the most appealing lecurer/assignment structure, because these things a liable to change.