...Depends.
What is your plan with them?
As Sami says. C919 is a very capable plane, very cheap to operate,
and to lease. Though it lacks range, and does not have a larger version. So you have to ask yourself 2 strategic questions :
- do you have a lot of destinations beyond 2400NM around 150/250 demand?
- do you have a lot destinations below 2400NM where 150 seats are not enough?
if you are not sure, C919 will cost dramatically less to operate. But you can't answer those questions if you don't make a preliminary full study of your market.