Decide between Postgresql and Mysql (help of comunity)

Hi,

I'm a Postgresql's user and I think that it's very very good and
robust.

In my work we're confuse between where database is the best choose:
Postgresql or Mysql. The Mysql have the reputation that is very fast
working in the web but in our application we are estimating many access
simultaneous, then I think that the Postgresql is the best choice.

Am I right?

Our server have 1 GB of RAM, how many users can it support at the same
time with this memory?

Thanks in advanced

Marcos