Staying in both City Centers during my travels and am wondering what you think is the easiest way from Dublin to Liverpool?
The easiest way is to fly and the good news is that it's cheap and the bad news they are cheap because they are all on Ryan Air. A random non-weekend day in summer is about 20 euros plus whatever fees Ryan Air can find to tack on. As long as you carefully read all the conditions and follow them you can fly for the advertised fare.
Good luck,
=Tod