Also important to consider where you are based, what cabins you generally are booked into and what airlines.

Most airlines tend to treat there own FF's slightly better than those of other programs in the alliance (particularly with respect to opups and issues). You can also generally only upgrade a flight using points of the metal carriers program

(eg. whilst you can use BA Avious points to book a redemption on a QF flight, you cant use BA Avios to upgrade from Economy to Business on that flight).

On the expiry there are two types - one where each individual point has a defined life (eg 3 years) with you spending oldest points first (eg. SQ Krisflyer), and others where any activity will extend the life of all points (e. QF)