I have tried all three types I guess and I think it pretty much depends on the type of villain you chose, which way works best (or which way works at all)
I had the last minute revelation, because I kept leading on my readers, making them think it was Tempus when it was someone totally different after all. For the sake of surprise ( and to my own amusement this was pretty good
)
I used Lex Luthor. I think with this guy it was a mute point to leave him covered, unless you use a later Lex-should-be-dead-but-isn't version of him. I think revealing the villain at once gives you the opportunity to concentrate on Lois and Clark getting out of his trap.
And in my latest story the villain is revealed in the middle of it all. Though somehow I've seemed to make a mistake, because people seem to think that the villain is still someone else.
Personally, I like it, when the villain's motivation is clear. I love to solve a mystery, but sometimes it's good if you know more than the characters. If you know the villain is up to something, you can keep biting your nails what will happen to LnC
