Upgradeable fare buckets-what's the best deal?

All,
Today I should be able to get return flights to Miami for January 16.
Trying to spend a minimum of money and then upgrade with miles.
So best options for you?
M fare and miles or S fare and miles?
Or anything else ?
Not enough miles to pay with them only.
All advice welcome.
Thanks!

M then miles is cheapest, but S will cost you fewer miles and guarantee you're at least in PE if you can't get Gs. Remember there's no guarantee that Gs will be available as soon as flights go on sale.

Indeed Gumshoe and I will make sure availability is there before I book...
Just realised that I would be short of miles with a M... S it shall be then
Hopefully can get a decent price for them...
Any chance of prices going down if I wait a bit?

Not really - they may fluctuate a bit but it's only the cheapest fare buckets that are included in sales.

If you've the time and the inclination you'll probably find an ex-EU UC fare is cheaper than an S. I'm seeing £1161 starting in DUB next January which would earn you full UC miles & TPs, not cost you any miles and guarantee you UC. Even the cheapest PE fare is coming in at £1158 so an S would be several hundred more. Ex-EU isn't everyone's bag but it would almost certainly save you money.

How do I get a fare from DUB?

Expedia. Choose virgin as preferred airline.

Also to note, probably better to choose a BA flight connecting, otherwise you get economy and no lounge in Dublin. Also, I'd choose the option to overnight in London. I personally check in 3 hours before transatlantic flight, and it being the clubhouse in heathrow, tend towards at least 4 and ideally 5 hours before...