Why is the EM5 so much more popular than the GH3?

Give the GH3 sometime. And other reason is that Olympus users are more enthusiast about their brand.

I tend to stay neutral, I use Panasonic, but to me the OMD and GH3 are in the same level. Both superb cameras.

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Simplicity is the ultimate sophistication.
God always take the simplest way.
Imagination is more important than knowledge.
God is the tangential point between zero and infinity.
Aleo Photo Site