E71 - QWERTY, Bigger Screen, Solid build quality
N79 - Smaller & Candybar form factor, FP2, DLNA (uPnP), N-Gage, 5MP Camera, FM Transmitter, 3.5 mm jack
There are the points of difference i could come up with. All depends on what you want. Both are completely different, and the best devices in their Series. Decide according to what you want.