I am getting freaking emotional here. I don't know if I should do SN or exit bag. I know no one can tell me which to choose. I just wish I knew what to do. I need to do something.
The following is not any recommendations for you, it is simply how I personally balance the two methods.
The exit bag is a more appealing method to me. This is because I've never had any sound assurances that SN is painless, and I've heard reports that it's actually quite painful. And I hate being nauseous; apparently SN induces nausea, and this also increases the risk of failure/necessitates antiemetics (whose efficacy in combating the neausea, I'm unsure about). The exit bag method (using a simple asphyxiant such as He, or using CO) I've much more confidence in, because I've read from many sources that it's painless (or at worst causes minimal discomfort), although how accurate that actually is, I can't say.
Unfortunately, the issue is complicated by the possibility that different people may have different reactions to the same method, and a multitude of factors are at play which ultimately cause the experience to differ between individuals.
Really I wish there was more reliable information on the different methods regarding the exact death experience, but that's hard to obtain, of course.
Are you sure about there being no long term effects of SN in the event of failure? That sounds too good to be true, although it could certainly be true, I'm just skeptical. And indeed, the risk of exit bag failure is daunting, and a great deterrent.