I assure you from four years of wordpress experience with MANY of my sites on the first page of niches with millions of competitors, it does not detract dramatically from seo rankings. As far as .php, that is OK for developers but not really necessary. Most plugins are hands off. Perhaps changing a header or footer code might be helpful. But that kind of change is so simple to do if you can't use notepad and look at a youtube video for instruction, you probably need to be in another field of work if you cannot master it.
I appears that this man is a developer. Another umbilical cord to a "client". Wordpress is all about empowering people to do work that was once the domain of "developers" who, very often, do not deserve the badge.
I've used all three. I can agree that if you are a programmer, you'll probably like Drupal more. wordpress is just a blog platform to me. It seems any time you make it do anything else you really end up shoehorning in that extra functionality.
I tried out several platforms and Joomla has worked best for me. First I can manage multiple sites across a lot of industries with ease. There are plug-ins for practically everything. Making a custom template can be easy IF you are a DreamWeaver user who was lucky enough to buy the Media 65 kit before it went away. Manually it can be a challenge.
The other thing I like is using Joomla as a basis for ecommerce sites. You don't end up with a ecomm site that can't do anything else or a normal site that can't do ecomm well.
No matter what, they are all resource hogs, so you have to be ready to step up the hosting if you want a site to perform well. You can also check out some other options at cmsmatrix.org. Or drop these three into a compare and see what you get.
There are so many CMS platforms on the market. Choosing a system that works best depends on your needs. wordpress makes it easy for non-technical people to manage simple websites. However, I would not consider it for business because its functionality is too limited. Joomla seems easier for end users than Drupal or Dot Net Nuke but both have issues. SharePoint is another option. It's powerful, cheap and extremely extensible.
We use several and choose a platform based on our customers specific needs and experience.
I have to agree with much of what some others here have said. Here's my two cents worth:
WP is very inutuitive. You can teach any receptionist or mail clerk how to build/edit a post or page in minutes. Unless you're really anxious to preserve a dependency for every minor alteration, WP is the quickest and easiest for both you and the client, IMO. That said, it does have its limitations as a CMS. It will handle a 10,000 page site, but not as efficiently as either Joomla or Drupal. I have used it for 1,000+ pages, however, with very good results. It just doesn't scale as well as the other two.
Also, the concerns about updates causing you to face either loss of customization or sacrificing security are easily overcome by the use of a child theme (essentially a theme within your theme), which won't be affected by any updates, thus protecting all your customization.
Joomla is much more complex to learn, and I find it to be counter-intuitive in many regards. Maybe that's just me, and the fact that I'm so familiar with WP, though. I have played with Joomla a good bit, and regularly post on a couple of sites using that platform, and still have problems with it nearly every single time. The curse of old age, maybe?
Drupal is also difficult to learn, although slightly better than Joomla in that regard, IMO. I find it about equal in terms of intuitiveness, and perhaps even more difficult to teach a client how to manage his site. The only major plus of Drupal over Joomla, for me, is that Drupal 7 incorporated RDFa into the platform. Unfortunately, RDFa may fade, if schema.org takes deep roots.
As was said, there's no pat answer... so much depends upon your situation. I guess my opinion would be that you're best to consider wordpress if it's practical from a scalability standpoint.
Looked at Drupal a few years ago now; thought it good but reckoned our clients, who are mostly not tech savvy would find it very confusing. Most of our clients find Joomla pretty easy to use.
We tend to build custom templates for Joomla - although there are zillions of good templates out there, just find customising them to suit a client takes longer than building from scratch, and you end up with a much lighter weight template that you can easily maintain going forward.
We do use Wordpress for blogs , but really don't find is as comprehensive a framework as Joomla, so Joomla would be my first choice for something more than a blogging platform. And of course if you need a blog as well you can run Wordpress in parallel or even use the Wordpress for Joomla component that integrates a Wordpress installation into Joomla. Sounds a bit bizarre, but works pretty well!
www.dvisions.co.uk - lose the camouflage and stand out...
One thing to keep in mind regarding Drupal vs. Joomla is that the modules in Drupal are Free. I believe you have to pay for a lot of the add-on's in Joomla.