Leviathan looks to be the best, judging from the layout and general opinions of people who've ridden it. From the three I've ridden though:
1. Steel Dragon 2000 - Absolutely not just "another airless Morgan". Admittedly, it doesn't have the most inspired layout, but the height, speed, length and airtime on the returning bunny hills more than make up for it. The traditional, slower lift hill also provides more anticipation and offers great views.
2. Millennium Force - Fantastic first drop and a fun ride after that. Much better than I'd been led to believe.
3. I305 - I wasn't a fan. It's hard to put my finger on, but it just didn't click with me. Granted, I rode it with the trimmed first drop.