I have to disagree where joomla is concerned.
If you want yet another joomla website then joomla is for you, if however you want to absolutely be original, custom fields, forms, usergroups, etc etc and basically be able to build a unique website that has exactly what you want,being displayed when, to whome and how you want then joomla is not for you.
If you are not very familiar with php you will run into a brick wall with joomla quite quickly because the plugin you want will not exist.
I recommended drupal because with just a few select plugins you can create any conceivable layout / input fields.
Joomla has some very nice skins, some nice plugins too.
You can create your own plugin if you choose and if you can.
Drupal has all of the above, but the ability to rearrange, amend, add, remove anything you want, text box, file fiends, drops, checkboxes, forms, permissions, for ALL content is easy on drupal, but very difficult on joomla with custom code being the only real solution... If custom code is the answer why use a cms in the first place?
Then you have the joomla / mambo split. Incoherent instructions, incompatible plugins, blurred lines between official and non-official support sites and the fact that many of the plugins are commercial... BUY to TRY.
My own experience was as follows.
Joomla was ideal for the first attempt. Easy to get an out of the box website that has a few 'common' features, forum, blog, gallery.
When we began needing more. more features, more flexibility with usergroups, more custom features then joomla became restrictive, incompatible, expensive and basically a 6 months mistake.
When you have absolutely no clue what you are doing joomla is a good start, but be prepared to abandon it.
Drupal is just as good for the first timer, but it is also built to last.
when all is said and done there is the good old 'personal preference'.