The DB/SL is a very handy and adaptable machine, giving you more than just a lathe. The versatility is built in, not added as an afterthought. Then you can re-configure it to do many other jobs. But, it lacks rigidity and capacity when turning.
The U3 is better for turning, but only as versatile as a conventional lathe. The U4 is just a variant on the U3 - not significantly different in machining capacity or performance.
The PC is not much use today, as the electronics and computer requirements are very obsolete, but the Basic looks to be a solid machine, and has places provided to attach stepper motors and other components for NC use. I'm hoping that, with modern stepper motors it can become a useful NC machine.
In all cases a weak point is the motor - better replaced by modern permanent magnet types which pack more power into a smaller space with less heat and noise. There are plenty around for the DB/SL and U3, but for the PC/Basic it is more difficult due to the small size of the original motor. It would also be necessary to replace the speed control electronics, but that would be no bad thing.
So it's back to horses for courses. If you only have space for one machine get a DB/SL. If you only want turning, get a U3. If you want a more complicated life get a Basic, or a PC, strip off the stepper motors and find a better motor for it.
I have been in, or am in the middle of, all three situations.
