Usually for sciatica the recommended progression includes nerve gliding exercises, back unloading exercises ( e.g. alternate knee to chest ) along with extension exercises ( e.g. McKenzie extension protocol for centralizing the symptoms).
I went through all the videos and they seems to be useful depending upon the stages of sciatica. For example, sitting position increases the intra-discal pressure and can result in increase symptoms so it should be avoided during the acute/initial stages of Sciatic pain. A lot of factors may contribute to the symptom and ultimately the outcome. For example, individual with postural variation and in cases of hyper-extended back / hyperlordosis, more focus should be on unloading the back i.e. stretching of hip flexors, hamstrings and calf muscles etc.
General recommendation includes:
1. Nerve gliding exercises in supine position i.e. 3-4 pillows under lower leg of the affected side and perform ankle dorsi-planter flexion followed by pillow under the knee and perform flexion-extention of the knee ( 2-3 minutes).
2. Back extention exercises protocol i.e. starting with prone lying–> prone lying with pillow under the chest –> prone on elbows and so on.
3. Unloading exercise like alternate knee to chest progress to double knee to chest etc.
I would say for initial stages: 1st video http://youtu.be/ionNNMvBUgo is good , as it describes correct positioning followed by unloading the back, which is useful during acute stages of sciatica, but caution should be taken with double knee to chest.
Last video includes the concept of centralizing the symptoms ( general extension protocol ) http://youtu.be/ionNNMvBUgo
http://youtu.be/htgyPKNHUls :this video includes nerve gliding techniques, but in sitting position. One should progress from supine position to sitting especially during initially stages and after achieving adequate back muscle strength one can progress to sitting position.
Unfortunately, there is no set protocol that fits every individual due to anatomical and individual variations. So, its better to start with the safest position and progress accordingly.