Okay, here's my list, in approximate order:

Pink Floyd
Neil Young
Led Zeppelin
Dire Straits
Bob Dylan
Fleetwood Mac
Lynyrd Skynyrd
Deep Purple
Mark Knopfler
Wishbone Ash

Where I have a strong preference for era:

Fleetwood Mac - The 1970s albums with Lindsey and Stevie
Lynyrd Skynyrd - Ronnie era (up to 1977)
Deep Purple - Mk2 line up with Ian Gillan, although I like Mk3 as well
Wishbone Ash - The 'Argus' line up (1970-73)

I'm sure you're all deeply shocked at my #1 choice. Not. I found it relatively easy for numbers 1-8 on my list. It's difficult to explain, it just seems right to me. The trickiest choice for me was who to put fifth. My head said Bob (as I love more of his music), my heart said Fleetwood Mac (Rumours was my first musical love)! I considered putting Knopfler's solo works in with Dire Straits as I feel they are the same musical journey, but I think there's enough I love from his solo albums to get him in the top ten as a solo artist, for now at least.

Tenth place was the hardest one to decide - I ultimately went for Wishbone Ash, but I also considered Rush and Genesis.. These are my honourable mentions, if you like. Both Wishbone Ash and Genesis have one album I really love (Argus and Selling England By The Pound), but I have to be in the right mood to really enjoy most of the other Genesis albums, even from my preferred era (up to Steve Hackett's departure), whereas I can enjoy Wishbone Ash most of the time. Rush have two albums I really like, but I haven't listened to anything else by them, whereas with Wishbone Ash I know their early era well. It's weird because there are other artists whose catalogues I know better than some of these, but I don't like them enough to put them in my top ten.