Auto Europe or Conn

I've used Conn's twice and have been quite satisfied. I pick up at the South Circular Road location in Dublin and drop at the airport. No drop fee. I find the pricing to be transparent as well. They have a US phone number you can call with questions and while usually no one answers, leave a message and the call is returned promptly. I know a lot of folks here like Auto Europe. They're probably fine too.

Haven't used Conn's yet, but I do have it bookmarked for a future trip based on a prior recommendation by Trotter. It does look like a winner.
We've previously used AutoEurope from Dublin Airport... which has usually been Hertz in our experience. The airport locations open as early as 5:30 AM, whereas the Conn office doesn't open until around 8:30, so if getting an early start is important to you you'll want to be aware of that.
The airport concessions are handy if you're arriving super early in the AM ... which my arriving flights usually seem to do.
If heading south or west from Dublin then the Conn location would be quite handy.