Many people say to buy the biggest you can afford. I say buy the biggest you can move. If you have a right equipment at had you can move big lathes. My baby lathe can be picked up and moved about quite easily by me but it has a maximum working diameter of about 3.5". That is fine for me but sometimes I wish I could go much bigger. For example I had an unevenly worn disk brake rotor and I would love to have put it in a lathe with a grinder attached. Instead I had to bolt it to the bench and grind carefully by hand with an oil stone for 5 hours. If you know what sort of projects you will work on then you can match them to a lathe size. If you are not sure but have the workshop space then do as Ratranger suggested above. Also, some lathes have a small section of the bed near the chuck that can be removed to allow even large items to be worked on. Check you electrics to see what horsepower motor you can run - approximately 750 Watt is 1 Hp. If you buy one and it proves to be too small you can always sell it and buy another. The resale prices on lathes is excellent so you do not lose much. I have done several repair jobs that saved we more than the lathe cost e.g. I repaired a Hitachi carburetor 2 years back because parts were not available. Buying replacements carbs have cost more than my lathe cost.
Hope you have the bed to mount all those bits on!
Hope you have the bed to mount all those bits on!
Good thing there's no room in the garage...
https://flint.craigslist.org/zip/d/lapeer-lathes-mill-drill-presses-heavy/7157232749.html