I have a soft spot for Helsinki - I was there last December and the operators actually offer a self-guided city tour leaflet for tourists so you can catch one of the routes which form a figure of 8 around the city centre and follow the sights from your window.
Helsinki certainly has a feel of an "older" tram network, much of it on street. Have seen it run through a blizzard few days as if that was nothing unusual. In contrast the Helsinki Metro, just one line, seems a bit pointless. The whole system doesn't really carry heavy loads.
Another favourite system of mine is Milan, where there is still a very large fleet of 1930s cars which just seem to go on and on, mixed in with various newer ones, and again is a traditional on-street network.
I haven't been to Vienna for many years but I get the impression that it hasn't changed a great deal, and certainly is a big system.
In Russia, St Petersburg, which once had the largest network in the world, is now a sad shadow of that, many routes abandoned and the cars and trackwork in poor condition, with the remaining routes a random arrangement (it reminds me of how Philadelphia USA's system went in the 1970s). Almost all the cars are still Soviet era, a few with new bodies or even just new front ends, and patronage has fallen way off. In contrast the Metro in the city is well planned and run, and handles huge loads all day.
If you include systems lighter than mainstream Metros, then London's DLR has to be up there for efficiency and handling the loads.
