ZS Associates vs. MBB for Life Science Consulting

Hello - I joined ZS Associates as a Manager 6 months back in India office. Before ZS, I worked in Technology (think IBM, Deloitte, TCS). I have about 10 years of experience in Pharma/Life Science. 

The firm seems great. The work is challenging and the opportunities are amazing. I truly want to remain in Life Science/Pharma. My question is how different is the Life Science division of MBB/ATK/LEK/IMS from ZS? I have heard ZS is pretty solid in Life Science/Pharma; how tough is to lateral to MBB/ATK/LEK from ZS? 

I am not looking for prestige per se. I will be an Associate Principal in 2 years and Principal in another 2-3 years. But, I am trying to figure out the differences between various firms (only for Life Science). 

Thanks!