If you go with a coaster, (I wouldn't but YMMV) get a new one with the 175mm axle. The brakes on the old ones never worked worth a darn. I have a friend who uses a front caliper and new rear coaster on an old steel Raleigh frame and he loves it.

If you don't want a coaster, there are pros and cons to new vs old.
The new ones work great and you can get longer axles, but you can't get the newer parts. Fortunately many of the old parts like springs, pawls, gears, cones etc. fit.

The old ones also work great but you can get a false neutral if you let the cable adjustment get way off. And they are more efficient due to running oil instead of grease. And, oddly parts are readily available if you ask on such forums.