Well, I voted for S4, but I would have voted for S3 too if I'd been allowed. Basically, I like them being together, with Lois knowing the secret. Why? Because I like seeing Lois supporting Clark, acting as his confidante, etc. It also gets me away from that whole "will they/won't they" thing, which almost every show with a male and female lead eventually gets to and then does ad nauseum. The downside is that Lois has less spunk in S3/S4, but on the other hand, Clark looks particularly yummy in these two seasons.
I'm like Labrat - I watch the show for its special moments, rather than whole episodes. It doesn't bother me, therefore, if the plotline stinks or there's the occasional out-of-character moment. I'm so un-episode orientated, in fact, that I'm not even sure if they *were* actually together in S3 - and don't ask me to name episodes or give you their plots in a nutshell. I'm on the 'Friends' level of episode identification, as in: I like the one-where-Clark-gazes-sadly-at-the-crib-his-parents-sent-him, or the one-where-Lois-and-Clark-are-sweeping-up-leaves-and-talking-about-what-keeps-their-relationship-going.
Yvonne