It would have been GREAT if Clark did not propose until the end of season three. The sexual tension between those two was completely addictive! I always felt that the romantic relationship between them was rushed and that is reflected in a number of fics.
Of course, if John Shea's character had not been killed at the end of season one it would have been fun to watch Lois' relationship with Lex crash and burn. Ah well, we will never know ...