PCUI/BSP vs JAVA iviews?

Hi

I installed business package for crm and i am planning to develop some new iviews. Rightnow I am confused to decide on whether to develop the iviews in java or in PCUI/BSP?

could some one please let me know what is the criteria to decide which one should i use?

For ex: why did SAP choose com.sap.pct.crm.mkt.Calendar (Marketing calendar) iview to be developed in java, why not use pcui/bsp as used for most of other iViews in the business package?

Please help me in this regard.

Regards