Day Two. Where the action is.
I suppose saying "Torchwood" is cheating? Ah well. It was worth a shot.
I think all three series that we've seen so far have a lot to recommend them. S1 introduces us to the characters. We get to know them as the dynamics of the group develop. We see their strengths and weaknesses come into play in plot-critical ways, and on reflection, almost all of those strengths and weaknesses come down to love. Especially the weaknesses. By the end of S1 the show feels really well established. We know these people now. More importantly, they know one another better than they did when we started. Jack's immortality is no longer a (badly-kept) secret to the team, everyone's sins are laid bare by Bilis, etc.
And then Jack has a big adventure on Doctor Who, in which the team has really only a tiny part because, well, watershed.
S2 is strong because we're picking back up from that point in S1. We come into it with a Torchwood which has become more effective out of necessity in Jack's absence. Relationships have become more equal. Ianto, who was "just the teaboy" in S1, is now kicking in doors by Owen's side. Gwen, the new girl, has been in charge. That left a lot of room to try other kinds of conflict, tell other stories, and explore in ways that weren't just about establishing the team or doing exposition. Which, by the time we get to Fragments, makes that realization that we didn't know as much about Tosh, Owen, Ianto, and Jack as we thought we did, kind of brilliant. By the end of S2, we've been dealt a massive, destabilizing blow with the loss of Tosh and Owen.
And then everybody gets to be on Doctor Who, and we see explicitly that being a three-person Torchwood is very hard, and even more dangerous, and that Gwen's a pervy Ten fancier like the rest of us.
Children of Earth pretty much hits the ground running from there. What we thought was difficult and dangerous before gets exploded, if you'll excuse the pun. We see Torchwood's real place in things, as well as their ability and will to fight back against enemies on all sides. We find out more about Jack's past, more about Gwen's future, and even more about Ianto and his life. Even more than S1 and S2, which were written in such a way that they could actually be "over" by the season ender without too many threads left hanging, we're left wondering how on Earth things could ever be put right for what's left of the team. Which is at this point, basically a very pregnant Gwen, with Rhys in tow.
And then we see Jack on Doctor Who again, and RTD massages our uniform kinks with a moment straight from the most uniform-kinky vaults of Rule 34.
So yeah, this is another really difficult question, because I'm genuinely very happy to watch any of the three. If I had to choose one for having everything I've loved about the show thus far, though, S2 would squeak in by a very narrow margin. There's a lot of story in S2, we still have the original ensemble cast, and for the most part it's really satisfying viewing because it's stories about characters we're already reasonably expected to know something about. Fewer formative moments, more kicking ass, basically. And, of course, the requisite amount of crying at the end. Seriously. I need hard alcohol and a box of tissues at the end of S2. In abundance.
Day 01 -
Your favourite Torchwood memberDay 02 - Your favourite series
Day 03 - Your favourite episode
Day 04 - Your favourite alien
Day 05 - A scene that made you cry
Day 06 - A scene that made you smile
Day 07 - Your favourite quote
Day 08 - Your favourite cast member
Day 09 - An image that makes you smile like a git
Day 10 - You favourite promo picture
Day 11 - Your favourite couple
Day 12 - Your favourite couple scene
Day 13 - A piece of music you love from the series
Day 14 - Something you’d like to re-write in the series
Day 15 - Behind the scene video that made you laugh the most
Day 16 - Your favourite outfit
Day 17 - Your favourite Gwen moment
Day 18 - Your favourite Ianto moment
Day 19 - Your favourite Jack moment
Day 20 - Your favourite Owen moment
Day 21 - Your favourite Toshiko moment
Day 22 - Who you’d shag, cliff and marry
Day 23 - Your favourite Torchwood website
Day 24 - A Torchwood geek moment you’ve had
Day 25 - Your favourite Torchwood fan-fiction
Day 26 - A piece of fan-art
Day 27 - A fan-video
Day 28 - Your favourite location or set
Day 29 - Where you think the series should continue to
Day 30 - Best Torchwood on Doctor Who moment