Which Mac is the best deal for editing photos?

I am going to migrate away from windows. Which Mac is the most cost effective with longevity upgrade ablity. Leaning towards used Mac Pro.

When asking about a Mac desktop with longevity upgrade ability, that means the Mac Pro. The 27" iMac is a nice machine with a great display and its memory can be upgraded, but that's the extent of it. The iMac 21.5" models are not user upgradeable. The latest Mac Mini is actually more upgradeable than an iMac. (hard drive and memory) But you would have to supply a monitor, keyboard, and pointing device.

You also mentioned cost effective. A late model Mac Pro (depending on its configuration) can be expensive. And a new Mac Pro (2014 model) can easily exceed $3500, again depending on its configuration.

Thanks for the reply- I was thinking along the lines of a used Mac Pro-2011-2012 I found some with quad core / eight core processors and a $800- $1200 price range.
This should get me into something powerful enough to edit some big photos and flexible enough to grow later. I have a good monitor keybord and mouse.
It has been years since I have used a Mac can you recommend a reference book to bring me up to speed on operation and terminology of the OS and apps?

If you already have a decent monitor, hard to beat a Mac Mini for value. My 2012 model easily runs Photoshop CS6.
Another option is a 15in MBP. Plenty of horsepower there. I sometimes drive a 27 monitor off mine as a second display. Again, Photoshop etc no problem.

EDIT: a 2011 - 2012 Mac Pro for $1000 would be an excellent photo workstation.

Here is a good book IMO
http://www.amazon.com/dp/B009A11C5W/?tag=macforums0e4-20

I like The Missing Manual. You can get this for any version. The one for Mavericks just came out this week.

OS X Mavericks: The Missing Manual: David Pogue: 9781449362249: Amazon.com: Books

Mac Pro with say 16GB of memory and an SSD drive.