Once you get out of PHP-land, there's not that much difference. The dividing lines are in what portlets are available out of the box and how much you want to spend. The rest is about who on staff has skills to administer what or who feels up for a new challenge. For me, I go back all the way to BEA Weblogic some years back before Oracle bought them. But Tomcat, JBOSS, Oracle's Application Server, SunONE, and others have been in and out of my life.
I know a lot of IT peeps who get one tool and then try to do everything in the world with that one tool. The old adage about everything looking like a nail when all you have is a hammer.....
I really like Liferay. IF you want the good, the bad, and in some cases, the old and outdated, check that thread out. I'm a bit of a loner in being a Liferay advocate. I'm also a realist and I know that Liferay isn't always going to be the perfect choice for every shop and every combination of technologies on the planet. There are going to be times when you *should* pick something else.
Once you start to talk about integration, I think a lot of it depends on what will play well with your other systems. Since I have no idea what else you have to integrate with, you'll have to judge that for yourself. If you're a heavy Oracle Shop, then run Oracle's Application server. I say that simply because it will likely integrate easier with your existing applications. Oracle's stuff is exceptional in this regard. So if you're running Oracle Reports, Oracle Financial, etc. it will all just sort of "suck" right into the App server without a lot of tweaking and tinkering. In that regard, Oracle is slick as snot on a doorknob. You will, however, have to pay dearly for the privileged. Then the question becomes, is it worth it right now? Will it be worth it in the next 3 to 5 years? Will the cost of EE and custom development in Liferay be equal to or greater than the cost of Oracle? If the answer to that is yes, then you should pick Oracle. The same applies to SunOne or any other application/portal server.
The other consideration is the presence of some "must have" feature in one platform that isn't present in the others. Does IBM do something for you that no other application server do? Or EBA? Or eXo? or Weblogic? or Websphere? or some other product? Then, by all means, choose that.
However, it sounds like your customer isn't currently running a lot of "heavy iron" applications. If they've been running Joomla or Drupal, I can almost guarantee that they're not using a lot of enterprise level software. That being the case, Liferay is quite likely the most bang for the buck. And it will grow well with them over time. The 5.3 release is looking especially promising.
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