You have excellent taste. Here's my current top 10 off the top of my head:

1. Heavy Horses
2. Budapest
3. A Change of Horses
4. The Whaler's Dues
5. Minstrel in the Gallery
6. Moths
7. Toad in the Hole
8. Seal Driver
9. Flying Dutchman
10. Beside Myself

I left off "Thick as a Brick" and "A Passion Play" as they are something more than "songs". There are so many pieces I love and the list would be different tomorrow or perhaps an hour from now. I've loved Tull since I first discovered them in 1969 and have seen them over 30 times. Ian and his band are coming to Seattle in June and I'll be there as usual.