Noel can only play center period. He has no jump shot, he has to play under the basket on offense and collect garbage. This also allows his defender to play off him and protect the paint. While he can pass, he has bad hands and shouldn't handle the ball.
We really don't know that much about Jah, he's reshaped his body, has shown an improved jump shot, and has never really been coached up on defense (at Duke they basically told him to avoid fouling out because they wanted him available on offense). At this point, you'd be selling low, with no downside risk by keeping him (he's unlikely to play worse than he did as a 20 year old rookie) but loads of upside potential.
We do know about Noel, he's gotten stronger but still struggles to anchor against physical centers, is not a great rebounder like Thompson or DeAndre, he can run the court and block shots. Offensively he's a negative player. To me, he's the primary trade bait for a number of reasons:
1) his contract status (RFA next year, probably $80M for 4 years to resign)
2) his limited skill package, would be best paired with a scorer like Westbrook so he can focus on defense
3) his current value, could be a key role player for a playoff team