Originally Posted by
railways
If you want an all-train option and have money to spare, then:
Heathrow-Paddington
Paddington-Reading
Reading-Guildford
may well be faster than the above option.
You could cut out Paddington:
Heathrow-Hayes & Harlington
Hayes & Harlington-Reading
Reading-Guildford
still much slower and more expensive than the bus, mind.