I'm a bit biased, I like Meddings, but the Union looks as if it would be as good. As Fitzroy says, all about the condition of the machine.
I was very fortunate to find a good Meddings MF4/3. It is a brilliant machine. It has a gearbox and a quick change, 5 pulley belt drive. I can change pulleys in about 30 seconds, just push the release lever back, move the belt and re-tension by pulling the release lever forward.
It is a 3 phase machine, so I fitted a VFD which gives variable speed control. I have limited the VFD to stay close to the motor parameters, so I can get +/- 20% about nominal speed on each pulley. It has 5" travel on the quill. On the low gear and first pulley, if I could stop the chuck, I think the earth would rotate!!
The machine has a very convenient quill lock right at the front and a sturdy depth stop along side. Everything about the design makes it easy to use.
Main weakness are sacrificial pulleys in the gear box. If the drill has been abused, they can be damaged. They are still available, but quite expensive. My gears are a little bit worn, but the machine still works perfectly. The drill dates from early 50's. I rarely use the low gear, because I can get a range of 247 to 4800 in the high gear with the VFD.
The other hassle with my one is the lack of rack drive on the table, so changing the table, becomes a bit of a weight lifting exercise, but you do then appreciate just how solid these old cast iron machines are.
If you happened to come across one for sale. I would definitely recommend it, if it's a good model.