Live and Seconds Out, no contest - I grew up with 'em, and they still pack a punch/an atmosphere I haven't found anywhere else.
And Rainbow in third, of course.
I listened to TSL when it was released, and it was pleasant enough, but it never really registered, apart from one track - and I might be confusing that with something else: wasn't there a version of Firth of Fifth on that album? I seem to remember a rather divisive guitar solo by Daryl. Am I thinking of another album?