Hi Yonatan,
Yes, that can be challenging to decide which package to buy.
The first thing to start with in making a decision, as it sounds like you already know, is to choose which sensors to purchase.
There is a comparison of the sensors here:
http://www.somaticvision.com/products#sensors
The emWave trains only HRV.
In order to train with both heart rate (HRV) and skin conductance you need the IOM or Lightstone sensors (same function and quality, but IOM is white and Lightstone is blue). The Lightstone and IOM are no longer made by their manfuacturer, although we have open box / slightly used models available for purchase.
We have a new sensor that, the BioSignals HS sensor, which is similar to the Lightstone in that it measures both HRV and skin conductance, but is a new. The heart rate is more accurate, and the sensors are more durable and can be replaced individually (if you break the heart rate sensor, you can replace it separately, instead of purchasing a whole new device).
http://www.somaticvision.com/BioSignals
We also have a version of the BioSignals sensor that measures breathing (respiration) using a belt. This device is a 4-channel device, the BioSignals HS+ 4-Channel. It measures HRV, skin conductance, finger temperature, and respiration.
http://www.somaticvision.com/BioSignalsPlus
So, in short, you should purchase a package either with the Lightstone or BioSignals HS sensors, if you want to train HRV and skin conductance. If you want to also train respiration and/or finger temperature, purchase the BioSignals+ 4-Channel, which trains all 4.
Best,
Ryan Deluz
Somatic Vision Inc.