Star Alliance member Avianca is useful because it has an award chart similar to (but somewhat better than) United with no fuel surcharges and is a transfer partner of American Express, Capital One, Citibank, and Brex.
And right now through December 17, 2021 the LifeMiles program is offering a 25% bonus transfers from Citi, Capital One and Brex – but not from American Express. While the bonus may post as a separate transaction – it’s provided by LifeMiles and won’t show up on the transfer screen in your Amex, Citi or CapOne account – it should post fairly contemporaneously. LifeMiles says both the transfer and bonus will post within 24 hours.
This is useful if you have points spread across different transferable currencies since you can pool them in the same account. And LifeMiles has access to Star Alliance awards. Here’s a primer on getting the most out of LifeMiles and a warning why it’s much better to deal with them by email than over the phone. The program is great when everything goes smoothly online, less good when you need help fixing problems.