Travel from Heathrow to Salisbury

What's best for you depends on what's important to you. Price? Speed? Convenience?

Anyway, have a look at the National Express bus service: https://www.nationalexpress.com/en You get a one-seat ride from Heathrow Terminal 2 (where I think your United flight will land, but you should check) to Salisbury for under 20 pounds a person. The catch is that there are only a few departures per day, so you'll have to wait around until 3:25 pm (the next earlier departure is at 12:20, which I wouldn't want to risk if I were you, although you can pay a couple of pounds more for a flexible fare that should get you on the earlier bus if you happen to speed through passport control).

Among your other options are to take a bus to Woking and then a train to Salisbury (which takes about as long, has departures every hour or so throughout the day, but costs twice as much as National Express) or to take a cab (convenient but expensive).

https://www.thetrainline.com/train-times/heathrow-airport-(any)-to-salisbury

So either tube to Waterloo station then train to Salisbury or bus to Woking then train to Salisbury.

Salisbury is over an hour and a half drive from Heathrow so car service or taxi costly.

As Claudia said "Salisbury is over an hour and a half drive from Heathrow so car service or taxi costly." However, don't rule out a car service before checking out the prices. After a long flight, being jet lagged, and in a new place, nothing is better than a car service. For two people the price might not be that much higher than other means. We've found that car services based in the destination city work well as the drivers always seem to know the best routes "home". Google "car services in Salisbury U.K." and see what pops up.

Thanks to all of you - the advice is much appreciated! (As I spend more time with these tables, options, etc, - it becomes less daunting!)

Somewhat less, anyway!