No exact answer because it also depends what you are redeeming for
Biz class ticket?
First class ticket?
Economy class ticket?
Partner airlines ticket?
So it all comes down to what you are redeeming for, compare the cash price of the ticket if purchased outright, then compare to how much miles needed if purchase miles / amount needed to spend (AND ALL THESE ARE NOT TAKEN INTO CONSIDERATION OF PROMOTIONS ETC)
But basic rule of thumb, avoid economy class redemptions unless you really have to do it - go for biz class and above, 3 hours flight time and above
Always go for the higher class tickets whenever possible to maximize "returns"
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Additionally, I advocate for mindsets where you are redeeming the experience, rather than the convenience of the tickets
In another words, you generally won't spend money to buy a first or biz class ticket if you are not so well off; so normal people wouldn't have easy chance to come by to sit biz / first class. Therefore you should experience this kind of luxury made possible by your normal spendings. This is especially true if you want to take your parents to vacation or travel, chances are, if they are hardworkers in the past and living frugal life, they have never experienced such luxury. So as children, you may use your "bonus" to treat them for an pleasant experience on top of saving their poor backs from long flight durations.
But of course, if you have other priorities in life than flying with airmiles, then you would not be searching or asking through this thread anyways (cashback would be then preferred)
To be an airmiles fan, or even to maximize your returns via airmiles, you really have to do the non stop digging for your best rewards, and it takes alot of conscious effort to do it - one senior pointed out before >>> The original TS of this thread.
Thanks for your advice! I am currently earning 1.5% cashback for my overseas spending, not sure if it is worthwhile to earn EP instead.