I've spent very little time in either place, but I luurrrrrrved Edinburgh and thought that a week was a good amount of time to see Dublin, Galway and Kilkenny.
I haven't been to Ireland (forces keep conspiring against me). But, like stever, I also love Edinburgh. We spent a little over a week in Scotland this past spring and went to Edinburgh, drove up through the Highlands (visiting lots of little towns on the way to Loch Ness and Urquhart Castle- must do!), over to Isle of Skye (home of my favorite Scotch- Tallisker) and then down to Oban. From Oban, we visited the Isles of Mull, Iona and Staffa. Staffa was one of the most incredible natural formations I've ever seen. It's hard to say which part of Scotland was my favorite. All of it? It's beautiful, has tons to see and do (castles, hiking, horseback riding, general city ambling and more) and the people are so incredibly nice. We are actually considering going back next summer.
I'm your vote for Ireland, although I haven't been to Scotland.
We went to Ireland last fall via a travelzoo deal that included flight, rental car and hotels. We drove around the southern loop of Ireland hitting up "big" sites like Rock of Cashel, Blarney Castle, Cliffs of Moher (for the coastal cliffs) and Jameson, Guinness and more in Ireland.
We loved it! If you go, I would definitely recommend getting out of big cities like Dublin and Galway, with that I would recommend not staying overnight in the same hotel, taking day trips. This just seems exhausting and not worth it. There are tons of great packages under $1k, I'd look into that.