iMac i7 or MBP i7 with added display?

hi!

have macbook pro going on 4 years old , looking upgrade either mbp 15'' i7 or 27'' imac i7.

work university researcher , use both mac , windows applications - geographic information systems. love improve ergonomics of workspace adding desktop display - i've used mbp display until now.

mbp 24'' display or 27'' imac , use old mbp portable needs?

upfront!!!

 

what mbp have? if it's okay, imac

 

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