I think it depends on what lifting equipment you have available. The chassis without engine and gearbox is still a heavy lump to move and supporting the whole car then moving lifting equipment to separate chassis from body could be dangerous if you don’t have proper lifting gear. Think Health & Safety.
I would suggest it’s safer to lift the lighter body.
Remove as much weight from the body as is possible, all interior, door mechanisms, etc, taking as many photo's as possible as you do it. Believe bit me this is invaluable.
Then remove all body mounting bolts and carefully jack the body up. I use two hydraulic jacks onto blocks of wood positioned just inside the sills. Raise the body till it’s clear of the chassis then slide a couple of blocks between the body and chassis.
You now have many options for lifting the body clear. The method you choose will depend on space, available lifting equipment, supporting structure, height for lifting equipment and manpower.
I have recently trial fitted the body to chassis several times following extensive repair work. I did this single handed using ratchet straps attached to some roof beams, see pics.
This is cheap controllable and safe. Once the body was lowered onto blocks on the chassis I repositioned the straps through the rear turrets and round a beam in the engine bay. Final lowering is by the hydraulic jacks.
Dave