If Cloud is the future. Where will prefer to send their applications?

for small companies SaaS, for bigger companies IaaS & PaaS

 It's depends, in the concept of cloud computing SaaS consumes PaaS and PaaS consumes IaaS

The most of companies use SaaS in theirs production, to get a quick example of SaaS we have most of services pulished by google like google+, gmail, google drive

Thanks for the update.

Q: Why Big companies will not got to SaaS?  I know lots of big companies have already taken benefit from SaaS.

cloud was the future and future is here

question is not fully clear which service to use.

its what we may need if we have our own secure ERP or application we could be using either or cost effectice service to handle the loads or service or backups perhaps .

its the Budgets that drive the IT in many situations.

but if you have skillfull experts than having Infrastructure IAAS in the cloud is suggested so you know that how isolate you are and what are the vulnerabilities to  secure. else dont go near any of the service just relying on the big market player's writen disclaimers