Definitely not the Techno on a packed train, it's one of the biggest and bulkiest Maclarens there is! It's the wheels that do it, yes they don't wear down like all the others do, but they are much bigger.
If it's just for the nursery run, the Volo is the lightest. It has a mesh seat, and a carry strap, and comes with a rain cover. It's only downside is that it doesn't recline, so they can't sleep comfortably in it at all. But that might not be an issue if it's not going to get that much use.
I have a Quest, it's probably just the same when folded as a Globetrotter or Triumph, but has more features, such as a better recline system and an extending footrest. The brakes on the Quest are fine, mine is a 2012 model and it has improved brakes from the 2006 one I had so maybe some reviews complaining about the brakes are referring to older ones.
I love my Maclarens, I've had a Techno XT, two Quests and a Volo! I really wish I had kept my original 2006 Quest, I've never found one with a design I've liked as much (red hood, black seat with red outer and red and white circles on the seat. The hood was edged in the seat material too)