I'm going to be booking 2 PE return VS flights from LHR to SFO for November, but am wondering which fare class to opt for - either H class or S class. I'm looking for some recommendations from other members please
The H class is currently priced at £1,175, and S class £1,375, so basically £200 extra per person. The main benefit of the S class fare would be the potential to upgrade to Upper Class using air miles at the airport on the day, providing there is availability of course. Plus the extra tier points earned for an S class fare. I've managed to upgrade once before at the airport with an S class ticket, and just pay the £60-£70 taxes.
What would be your preference if you were in my shoes - would you go for the H or S class fares? For those who are more frequent VS flyers than me - are upgrades to Upper Class using miles on an S class ticket very commonly available at the airport on day of departure, or do you think I was extremely lucky to be able to upgrade that one time?
Thanks in advance for any suggestions!

The H class is currently priced at £1,175, and S class £1,375, so basically £200 extra per person. The main benefit of the S class fare would be the potential to upgrade to Upper Class using air miles at the airport on the day, providing there is availability of course. Plus the extra tier points earned for an S class fare. I've managed to upgrade once before at the airport with an S class ticket, and just pay the £60-£70 taxes.
What would be your preference if you were in my shoes - would you go for the H or S class fares? For those who are more frequent VS flyers than me - are upgrades to Upper Class using miles on an S class ticket very commonly available at the airport on day of departure, or do you think I was extremely lucky to be able to upgrade that one time?
Thanks in advance for any suggestions!