Need help pls

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Friends, have zeroed in on the following models for 42" led. Although am not sure whether to go for 3d or not. Need your opinion and share your experience for :
42LA6620, 42LA6200, 42LN5710
Between 6620 and 6200 does the MCI difference really matter ? If at all 3d is not required then is 5710 a good choice in terms of sound and PQ ?
Please help me decide.