In my opinion if you have expiring miles the best way is to transfer Citi's Thank You points (this requires the Citi Premier credit card) to combine with your existing points. Or you can transfer with a Capital One credit card if you have Capital One Miles but the transfer rate is 1:0.75 vs 1:1 which is much worse.
However, the redemption rate of Eva miles for the Economy Class is terrible. For example IAH<->TPE is 100k round trip for a free ticket in Economy class.
It is a better value to use the miles either for upgrade from Premium Economy to Business(40k Eva miles one way for IAH<-> TPE) or if available book a J ticket using all miles. (e.g. going from IAH to TPE would require 80k Eva miles one way for a free ticket.)

The availability of upgrades is much better than free tickets, though.

If you have a lot of expiring miles you can consider the above. Otherwise if you only have < 10k you can redeem for some magazines, sim cards or other small items. (mostly only useful in Taiwan.)