I suspect that RCs continue to be favored because a) they are traditional, b) they make for better story points, and c) they can't make the agent pair seem overpowered.

The main differences between TARDIS and RC are that the TARDIS is mobile in space and time and much, much bigger on the inside than it looks from the outside. The RC, on the other hand, is fixed in time (though it's HQ time, which is rather flexible) and space--you can't take it into the fic with you and bop around in it like you can with a TARDIS. RCs are also notoriously tiny, though some are better-designed than others. It just depends.

The thing is--and I'm revealing my bias here--a TARDIS pretty much eliminates the need for some of the usual PPC tech, like a portal device, and it also means that the agents don't run around through the story on their own legs, whatever shape those legs happen to be at the time. In doing so, it also eliminates many possibilities for an interesting (and funny) mission. If the agents can just sit comfortably in their TARDIS and watch what's going on around them, what fun is that?

That said, no one is going to stop you from putting your agents in a TARDIS if you want to when you have Permission... but it will make me sad if you do.

~Neshomeh, stodgy old traditionalist.

TARDIS' started to be used during the Macrovirus Epidemic because they were moveable whereas RCs are (supposedly) fixed locations. RCs are the norm, and the use of TARDIS' is recent, which is probably why you don't see many of them.

Not using one myself and not being greatly familiar with it all, I could be wrong. Best get a second opinion.

I sent the author a polite PM with my secondary ff.net account- the one that does not share my name- suggesting that she take the Mary Sue litmus test and offering my help. She replied with "Hi. I took the thing you told me to and I got 164. Could you be as helpful as possible and help me come up with ideas for my future stories. I really think that you'd be really helpful and all.. BTW, do you like any of the stories I wrote so far?" and I sent her another PM containing some concrit. I'm waiting for a reply. What I'm saying here is that this person may be open to help. I think she just put the "no negative reviews" thing on because she's gotten some spam from a troll called EdwardlovesJacob, among others. So what do you think? Should we try to help her before PPCing her, or is she beyond help?

Poor Rorschach... blowing him up wasn't enough? He has to deal with fangirls? I'd give him a hug if it didn't require standing downwind of him.