Yup, case in point. I was looking out for fares to TPE. Super Saver Economy costs around $500 and would have cost 30,000 miles. Therefore each mile is 1.6 cents. 4mpd card will give a 6.67% rebate.
But I prefer miles for the same reason as yywin, no need to track so many criteria or min spending and caps.
For Super Saver Economy, kindly subtract away the taxes, and just the fare part. Now with the new redemption, taxes are rather low, this is a good estimate, but esp calculated cost per mile, you should remove the taxes which is payable for redemption. One should also factor in the "limited" availability for redemption, whereas, if you are looking at Super Saver, it should be available immediate, though redemption tickets offer much more flexibility.
How to determine which is more worth it?
For example spending on Amazon:
1. using Citi rewards gives u 20x
2. using cimb visa gives u 10%
Personally, I'd rate the accrued miles at $0.01 per mile, for such calculations. It is easy to calculate and gives leeway for the other fees involved. So Citi rewards gives 20x or 8 miles per $, that is calculated at 8% rebate, while CIMB gives 10%.
Others will beg to differ on the rate, but with rebate, it goes into your cashflow, esp for the low spenders. With $900 spending, you get 18k pts or 7200 miles. Citibank transfer is now in 10k blocks (is this miles or points?). Anyway, you don't get the full 7200 miles in your Krisflyer account for redemption. But with $900 spend, you get $90 cash/statement credit, which you most likely will use up. This $90 can then be put towards the $500 ticket for use.
Miles game is not for everyone, unless you can spend quite a bit (assuming no expiring of your credit card points), or really know how to use your card.