This space is intended to be more of a community as well, so please jump in and share tips!
What is a good value to buy UA miles?
What is a good rate to buy UA miles for international travel (2 in business and 3 in premium economy)?
Any rate that is affordable to you and gives you a discount over the cash price while factoring in the loss of mileage earned.
UA is having a sale on miles at the moment, with a 100% bonus on purchased miles. This represents the best rate at which UA offers the miles.
Personally, for travel on UA or other Star Alliance partners, if there is saver award space available, LifeMiles may be a better option.
Consider the number of miles you need to purchase for each ticket, and how much you save compared to buying a cash ticket (also factor in what miles you may earn from buying a cash ticket). If buying miles comes out cheaper than a cash ticket, go for it. Depending on the route, you’ll save more money using miles for business class rather than prem econ
But of course make sure there’s saver space available on the routes you want, especially if you must fly on specific dates. We never recommend buying miles without a specific redemption in mind. But to David’s point, a friend of mine bought enough miles for a first class ticket more cheaply than he could have purchased a business class ticket with cash. (This was on AA/Cathay but the point holds regardless of the airline.)