I hate to sound like a grump, but this whole issue isn't really a matter of opinion since it was directly addressed by Tolkien himself.
HoMe X - Morgoth's Ring,
Myths Transformed contains his latest ideas.
Morgoth's original nature was greater, but his power was dispersed throughout all of Arda. Tolkien also tells us that a Vala's power naturally diminishes over time. The reason for this I won't go into. The point is that where Morgoth originally couldn't be contained by all of the Valar together (again, a Myths Transformed concept), he eventually came to the point where he was bound to a physical form and feared its death.
You can order cheaper paperback versions of the HoMe series (HarperCollins) at
http://www.amazon.co.uk . Not as nice as the Mifflin hardbacks, but cheaper and cool cover art. [img]smilies/smile.gif[/img]
[ November 21, 2001: Message edited by: obloquy ]
[ November 21, 2001: Message edited by: obloquy ]