Hi, I work for a transportation company and we are looking to buy 5 new computers. We will run a dispatcher software on all of them and they will connected to our server. The computer will be on 24 hours 7 days a week. Because our space is limited I was looking in to all in one computers but some people told me they are not good to be on all the time, the maintenance is more expensive and that they will have a shorter life time. Is that true? Or what computer should I get? And the software company said I can get any kind as long as they are 32 bit. Thank you

What do you mean all in one computers?

I wouldn't get consumer all in ones. But HP has a line of business class AIOs that should suit.

If the requirement is for them to be on 24/7 then it is what it is. It's a point that has benefits both ways.
http://computer.howstuffworks.com/question328.htm
You should not expect to get more than 4-5 years out of the systems anyway. I am not sold on the all in ones yet and I would suggest purchasing these models, which are also space savers. I would suggest the Optiplex line in the small form factor models, such as here.
http://www.dell.com/us/en/enterprise/desktops/optiplex-380/pd.aspx?refid=optiplex-380&s=biz&cs=555
You should always have at least one spare on hand anyway. And if you have a monitor go out, you would not have to pull the whole computer, just replace the monitor.