Pros and Cons...
MacBook Pro 15"
Pros...
3k retina isplay (yes folks 3k is actually a thing, lol.)
Portable
Powerful
Blazing fast Flash Storage SSD
New The Force Trackpad
New Graphics Card
Great Sound from Speakers
Cons...
Can be more expensive than Base model iMac (2499.00 with discrete graphics... 1999.00 without.)
3k display vs the 5k on the iMac(smaller screen real estate.)
2014 Intel Processor
Can heat up and cause loud fans to activate (it's completely normal but a little annoying)
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iMac With 5k Retina Display
Pros...
Very powerful
Better graphics card
5k display (much more screen real estate.)
Base price is lower than MacBook. (2299.00)
Full Desktop with Keyboard and Mouse included.
Cons...
No The Force Trackpad
No standard SSD option unless paying more for all Flash Storage, (also the SSD is a bit slower than the MacBook.)
No portability
At the end of the day it's about portability and screen size IMO. Yes the iMac is also more powerful and has a bit better discrete graphics card but IMO they are not as important than the portability and screen size/resolution. I almost went for the iMac due to the good price, but I liked the lighter MacBook and the new features it had. Either way you'll get a killer computer that will last a long time and will do what you need it to do.
Kal.