Since I am not an expert on the mechanical side of the vehicles, I will talk about overall the quality of passenger experience on those vehicles. Those in the review are only those in regular service, which excludes the LFSe now (which is an EXCELLENT vehicle but the way, much better than anything listed below).
Best transit vehicle (overall) of all of Quebec:
RTC LFS Artic HEV (possibly the best transit bus in all of Canada, it has a great-sounding hybrid powertrain, the engine can stop and start while bus is not moving, and it has frameless windows which make it so much better than those without).
Worst transit vehicle in all of Quebec:
This is a tie between STM SCRAP LFS 2009-13; and
Grande West Vicinity (although production buses are made in Canada, the company is based in China which makes horrible quality stuff; the prototype was made in China by the way).
Most comfortable seats:
4th-gen LFS on CIT Laurentides (those used on 8 St-Eustache and 9 St-Jerôme)
Least comfortable seats:
Those on STM SCRAP LFSes 2009-13 (TTC Orion VII has worse seats than the 3rd-gen LFS, because of the horrible legroom in the rear)
Best seating arrangement:
STO LFS Artic HEV (lots of seats while still enough space for 2 wheelchairs on the front)
Worst seating arrangement:
Again, STM SCRAP. They took away so many seats that it is horrible to ride in them.
Tie between STO 7901 and Detroit-powered Classics in the STO and Galland Tremblant
Yet again, STM SCRAP. They don't sound good anymore, they sound rather like vacuum cleaners.
Best transit livery (those that are in service):
RTC new livery from 2013
Best transit livery (of historic vehicles):
FHTCQ/Metropolitain Provincial 7296
Worst transit livery:
No doubt, STM SCRAP. Man I really dislike those arrows, they cover the windows and they don't represent the transit agency and the city of Montreal at all. The T arrow logo before 2009 is much better, at least it represented that it was a good quality transit agency back then, with good-quality vehicles like the New Look and Classic.
Best coach vehicle overall:
Autocar Préférence 2016 MCI J4500 (they even have lighted seatbelt signs!)
Worst coach vehicle overall:
Any Prevost H3-45 before 1998 with the much older interior (they are just dull and doesn't look good).