Guruji,
I know MiMH is better than Ni-Cd when considering overall. But have a look here:
Advantages of Ni-Cds:
1. Low self-discharge rate(1%) comparing to 5% of NiMH. So NiMH are not suitable for low current drawn applications which is important.
2. Stable terminal voltage during discharge period where an NiMH loses its voltage like a normal cell.
3. Higher discharge rate for rapid current drawn applications.NiMH fails here.
I can see NiMH is environmental friendly and comparatively higher capacity than Ni-Cads which needs more charging time.