Engine dyno vs chassis dyno

Chassis dyno for me. I put my car on chassis dyno last year, in 30 minutes picked up 40 HP. The adjustments were made to my Ignition box, and fuel pressure regulator. Would have taken all day at the track for same accomplishment. Also, unless you use the same ignition box and fuel pump and regulator off your car on the engine dyno, these issues would not have been seen. Most engine dynos have their own box and fuel pumps/regs. Granted, chassis dyno numbers are not as "Radical", but those are the numbers pushing you down the track.
Both are good tools.