I love projecting slides. Straight-tray projectors are popular in NZ, so I decided to concentrate on Leitz models. I mostly use a Pradovit P150 with a Colorplan-P2 90mm f/2.5. The Hektor-P2 85mm that P150's come with has so much field curvature that it's really only good for keeping out dust.
I sometimes use a pair of Pradovit Color 150's also with Colorplan 90's - one is an early type with the earlier 46mm polished alloy tube, another with the later black 42.5mm tube.
I prefer the quietness of the P150, but the Color 150's are superb quality machines and the earlier Colorplan 90's have a flatter field than the later P2 type.
I have a Pradovit C2500 with a Colorplan 90 and Elmaron 200mm but no hand control. It's a solid commercial-grade machine, but noisy. They were the standard slide projector at universities here for decades.
From the early 1960's I also have 4x Pradovit-n and 2x Pradovit-f. One Pradovit-n belonged to my father.
There is also a late 1950's Prado 500 with Hector 2.8/250mm & Dimar 4.0/25cm, plus a Prado-SM with a 2.5/12cm Hektor. The "Pradoseum" site has good pages on the ancient stuff:
The early Pradovit-n's are a thing of electro-mechanical beauty with the lovely snick-snick of the slide change mechanism, but the 12v tungsten bulbs are pretty dim compared to any modern halogen projector. The ancient Prado's are brighter, but run at frightening temperatures.
For medium format I have a Noris Trumph Halogen and a Rollei P66A. The Rollei at least takes 6x6 slide trays.
I used to shoot K64 & K200, but unfortunately Kodak decided otherwise. Perhaps Kodak's recent change of heart with regard to the profitability of film production will extend to re-introducing Kodachrome?
Their recent statement to the Times of India talked about promoting the "archival" qualities of film and Kodachrome is the only material to meet that criteria (under certain conditions).
If you are on a budget I would recommend getting a Leitz Pradovit Color 150 or 250 with the superb Colorplan 2.5-90mm lens. Many have survived and Leica can still fix them.
Any of the more modern Leica units, i.e. the P150, P300 or P600 would also be good, but you pay a lot more money for them. You can also find "IR" versions of these later models which is handy if you like to walk around the room when showing slides.