Advantage: E-620.
The articulated LCD display on the E-620 lets you hold and shoot the camera at odd angles and orientations, say, to shoot a self portrait, or to hold the camera low to the ground, at waist level, or high up overhead.
Be aware that you’d need to engage Live view on the E-620 to take advantage of this feature. In Live View mode, the E-620 will use contrast detection AF (autofocus), which will be slower than the equivalent AF performance on the E-P1.
Read more on Olympus E-P1 vs Olympus E-620.