Generally unless your team has 3-4 auto attack oriented people then redemption is better. Redemption is also better if:
- Your healing/shielding isn't AOE
- Your team is heavily focused on teamfighting
- The enemy is always killing you very fast.
If you have AOE heals and an AA focused team then ardent censor CAN be a better pickup, though you generally want redemption if you are going to get ardent since you can apply it in a big area.
Example of when you might pick up Ardent first:
You are playing Taric, so you have aoe heals and always heal/shield at least two people.
Your team is composed of an ADC (who likes AS), a mid laner like Yasuo or Azir (who like AS) a Tank top, and something like Vi Jg (who likes AS but isn't completely reliant on it)
Basically your team needs to really like AS and you need to be able to heal/shield in an area for ardent to ever be worth it over redemption. It is often worth picking up ardent after redemption though.