If there's a possibility the team has to choose just one current player to whom they offer a large extension, I'd choose Turang over Contreras pretty easily. Turang is the best player on the team, is younger and plays a position at which the attrition and decline rates are lower.
If they're able to sign Turang long-term, then perhaps Pena becomes a trade chip in the search for Contreras's near/medium-term replacement.