Of the 8 MLL's I've been to, I prefer:
YVR Transborder (like the views, aesthetics and big shower)
YYZ International (for all the reasons listed by other posters)
YYZ Domestic (fairly similar to YYZ Intl)
YEG (Nice small lounge... like the fire place)
While I think AC's done a good job of standardizing the offerings at its major lounges, I will say that the one that doesn't stand out for me is YYC. I don't like how despite YYC being an 'AC hub' there is no shower and I prefer the lighter, fresher aesthetic of YYZ Intl and YVR Transborder to the darker motifs of YYC.