I started with Mambo back a couple of years ago when I first got my DH account. Loved it. But was really disatisfied with any help I needed. Most of the time I posted questions on the board it took days (if I was lucky) to get a response. And if I was lucky the response was either not useful or insulting.
When DH provided Joomla I did my research and posted a couple of quieries on their board. Amazing difference. Not only did I get a quick response, but helpful and not condensending.
So, I switched my origional site from Mambo to Joomla. Backed up the data deleted the site, and Click … Zoooom! Joomla was installed.
So far every mod or component you can see for Mambo you can get for Joomla. And a lot of companies have switched to Joomla from Mambo.
I had a need this week to do an even mod with paypal for a client. Found about 3 vendors who want 20 - 100.00 for their product. A quick search on Joomla.org extension and I found a component for free.
Joomla now has about 450+ extensions and it is growning. Not to mention that documentation is slowly comming on line.
I never really did find good docs for Mambo.
Another plus is currently most Mambo extensions will work. The word is this will continue until the next major Joomla and/or mambo release.
I hope this helps.
For the money (what money) you can’t beat Joomla.