I have never used Sebastian but I have used Nexxus Emergencee, DRC 28 and Aphogee 2 Step.
Nexxus Emergencee~I prefer this because it's less messy and I think it's better when you have longer hair. According to the instructions you can use it every 2 weeks and somtimes I do use it every 2 weeks. It really depends on my hair and my mood.
Aphogee~hardcore and messy as all get out. When you have longer hair, it's hard to get the ends dry and they become stuck to your back, clothes etc.
DRC 28~real hardcore. Less messy than Aphogee.
The reason I do prefer Nexxus over the other two is because Aphogee and DRC 28 can be extremely drying so you MUST make sure you take appropriate steps to moisturize the h*ll outta your hair and that's a fact. Otherwise you are gonna have major breakage, defeating the purpose altogether. So if you are gonna use these two, make sure you deep condition for an hour, use a good moisturizing leave in conditioner and splash on some aloe vera juice/gel, S Curl, Wave Nouveau or whatever daily moisturizing agent you use......cause you will need it!