New Service revolvers are very collectible, and there's a premium for those chambered in .45 Colt. If you want a big Colt revolver, chambered in .45 Colt, I'd suggest you look for an Anaconda. They're not cheap either, but they're not almost 100 years old, and the mechanism is more modern and less complicated than the New Service.
For your dad, I'd suggest he handle a few models, and see what feels good. There are a slew of new compacts chambered in 9mm.