A system that I am currently testing is the MoviSens EdaMove. The system consists of a small device that can be attached to the arm, and two electrodes to measures EDA at the palms of your hand. The EdaMove uses the exosomatic method, by applying a 0.5V direct current, and samples with 32 Hz. An accelerometer is also included in the sensor, so that you can correct the EDA recordings for movement.
So far, the recordings are pretty good, but I haven't done any formal testing yet. Usability-wise, it may not be the best solution, since it is somewhat more intrusive than a wristband/watch.
Update: This is the fun part. Skin conductance is a measure of skin sweatiness. Unfortunately, the stickers that attach the sensors to the skin (similar to how ECG/EEG-reference sensors are attached) let loose when the hands start to sweat. This is even more so with many movements. For tasks that require much manual work or fine hand-movements, the EdaMove may not be the best sensor.
From the E4, I know that performance is not perfect, but it is okay. Benefit is that the E4 also includes an PPG sensor and accelerometer. Moreover, the E4 allows you to monitor the recordings in real time with their Android/iPhone app.
There are two major issues though with the E4. 1: It needs a good connection with the skin. If not, you could rather easily have missing data (especially so for the HRV sensor). The sensor should thus fit rather tightly. 2: Empatica applies some filtering of the data before you can extract it. It is not clear, however, to what extent it is being filtered. NB. The website states that raw-data is provided. Only the interbeat intervals (IBI), an HRV metric appears to be filtered.