Diesels vs Hybrid vs CNG Transit Buses

[REddyTrainer]

I know this probably has been hashed out many times on here. How do the the standard diesel, hybrid and CNG bus compare in operating cost and maintenance? 

I remember quite clearly that the MTA capital plan had no hybrid purchases, which was likely for a good reason, but it was then modified for what seemed to be public relations. The past decade of experience with likely the largest hybrid fleet in North America probably informed the first plans. 

In my travels I see that many places have gone full CNG. I know that in areas with lots of free land can build CNG depots in remote places. What has been the experience with the MTA?  I see that CNG buses don't have as long of a lifetime, which I think is because the tanks have an expiration date. How cost efficient are they in comparison with fuel cost? I know it should be much cheaper now with a clut of CNG. In terms of pollution they probably are the best bang for the buck considering operational efficiency. 

Sorry for so much in one question.