I'm going to limit this just to equipment I've actually ridden. There's plenty that I could criticize on aesthetic principle, and one that I could certainly criticize mechanically.
Siemens s200 built for Muni
I found these to be a vast improvement over the breda cars that succeeded the lovable looking, yet mechanically terrible Boeing LRVs. The seating in the s200s is much more comfortable, they are quiet, they operate extremely well. Also, I was very pleased they went with the paint scheme that I chose in a citywide poll they did before these were delivered years ago. I think they fit San Francisco very well and I look forward to riding them every time I'm in town.
KS SLRV
I was deeply impressed with Dallas's system, and these cars really shone well zooming around town in the intense heat while the air conditioning kept the car is icy cool. They also ride extremely well, and accelerate smoothly. I really found them to be far above what I was expecting for a light rail vehicle in this region. I hope fellow people who live in Dallas admire them like I do.
Translohr "Gadgetbahn"
The nation of France has been gripped by the Michelin monopoly for well over a century, and this is deeply affected all of its railroad infrastructure. France's insistence that rubber tired trains are a good idea because Michelin bribed them into thinking so has produced a wide variety of issues. Not least of which is the immense amount of microplastics which could have been completely avoided, if they hadn't used rubber tires on trains in the first place. It may provide a somewhat smoother ride, but of the expense of much more maintenance. This type of system is even more ridiculous with a monorail countersunk into the street that a bus type vehicle blindly follows. It is both more complex than a bus and less useful than a tram. Also a technological orphan, which means it will be very hard to keep going after the technology has flopped. Streetcars have a disproportionately long life compared to buses because of their mechanical simplicity, and this actively works against it. It's the most absurd, useless, corrupt, and patently dumb "innovation" to misguide city planners into wasting money on it versus tried and true methods.
What are some of your favorite light rail vehicles? Let me know in the comments.