The big choice is to go 'in-ground' or 'self contained.' I know he will be setting into a deck and not the ground, but an 'in-ground' spa is a spa shell with separate equipment, and usually a gas-fired heater. They can be run with no cover since they will generally cool down between uses and be brought up to temp by walking over and touching a jet button, or by a timeclock at a set time each day/evening. They cost most to run with no cover - and the cost to heat is a combination of gas for the heater and electricity for the pump to move the water from heater to tub.
A self-contained tub almost always has an insulated cover and is designed to be kept hot. The ability to just lift the lid and slide in makes it much more likely that it will get ongoing use as opposed to waiting for heat. But if money is truly no object - including operating costs for as long as he owns the tub - he could set the system to heat several times a day and the wait time would be minimal.
Once he decides if he wants a covered, hot tub at all times - or an open heat-on-demand tub, we can start talking about brands...
BTW - I have set up several HotSpring tubs to run on gas heat. We have a lot of folks with beach homes. They show up Friday and leave Sunday afternoon - sometimes not even seeing the home for a month at a time. So we take a line off the jet pump with two speeds and run it through a gas heater. The owner sets the spa temp to the lowest setting and the heater never comes on. The gas heater is set to their favorite temp for soaking, and all they have to to is turn on the jets - high or low speed - and within a few minutes the thing is ready to use. Once it gets hot, it can stay hot over the weekend by either setting the tub's thermostat to keep it at temp, or just hit the jets as they get in and it will gain the one or two degrees it may have lost quickly.
Also - this is a favorite of our customers who entertain groups of young folks - they can pile way to many people in, splash most of the water out of the tub, refill from the garden hose (or the shower head mounted over the tub in some cases) and the tub can be hot again in minutes.
8-)
