The phrase "a challenge to decide" is correct and usable in written English.
It can be used when discussing a difficult choice or decision that needs to be made.
Example: "Choosing between two job offers was a challenge to decide, as both had their unique advantages."
Alternatives: "a difficult decision to make" or "a tough choice to determine".
"At the time, you're a teenager, maybe it was a challenge to decide what he really wanted to do.
Apart from the cartwheeling delight of Ibaraki, it is quite a challenge to decide on Keane's best goal.
"The whole thing presents a challenge to decide what to do," explained archaeologist Michael Jones, of the American Research Centre in Egypt.
Considering that it's enough of a challenge to decide between an Italian oil from Tuscany and one from Puglia, do you really need to bother with the new Peruvian olive oil they're selling at Kitchen Market in Chelsea?
Our esteemed jury of cultural visionaries, academics, and talents had quite a challenge on their hands: a challenge to decide who would be the grand prize winner of Hack the Bells, and the recipient of $700 USD and have their work acquired by the University of California Berkeley and Anton Brees Carillon Library.
You gotta find your own way, and it's a challenge to decide that.
It is a difficult challenge to decide how droid data usage compares to the data from a refrigerator or thermostat.
There are so many challenges – first a group challenge to decide who'll compete for the upgrade and who'll compete for the downgrade, followed by two separate upgrade and downgrade challenges – that there's no room to breathe.
In the universal table model it is a big challenge to decide the number of custom fields (columns in table).
But he called it a "difficult challenge" to decide what to do with those who want to come back.
Without detail financial loss estimation, engineers have to face the challenge to decide whether a badly damaged building is worth retrofitting for sustainability, or needs to be demolished because existing loss estimation models are not based on the post-earthquake damage rating system.
