exhange server or google mail

I think you need to write down what is pro and con for both solutions, in my opinion if security outweighs efficiency, a self hosted and maintained Exchange server might be the better choice since you don't control the servers/environment GMail is using. But if you are managing your own Exchange environment there's a lot to consider, how secure do you want it, how redundant/fail proof does your Exchange setup have to be, will you need 1 or 2 (or more) servers in that case, what about anti-virus and anti-spam, backups, monitoring of the Exchange environment to ensure stability...

There's a lot to consider, there's also a third option, Office365, it's hosted Exchange sort of... But then again, is it better than GMail, more secure, flexible, some think so, it's another discussion of course.

Thanks @spravtek

as i understand the short answer is the Exchange Server is better than Gmail

Well, it depends on what your definition of better is, the biggest concern a lot of companies have with Gmail is that they do not have control, you don't know what Google does with your mail, concern for privacy and security. As where in Office 365 this is less so, it's more "secure" (mark the quotes :-) ) ... But, a self-hosted Exchange is (when done right) more secure and privacy is far less of a problem.

There are also a lot of companies that set up a hybrid system, keep some mailboxes on their own Exchange environment and place common mailboxes on Office 365 for example.

now i should compare between my own Exchange Server or Office 365