What method would you recommend?
Of the ones you mentioned, Sodium Nitr
ite (SN) is the most reliable, most peaceful, and most forgiving in case of failure.
It is most popular method on SS, with tons of information. See Stan's guide for SN. (Stan is verified successful).
As with any method taken by mouth, SN requires requires antiemetic pills be taken beforehand, following a timing sequence.
Antiemetics (AE) suppress your body's natural instinct to purge (vomit) anything poisonous you may ingest.
Most failures with this method are due to vomiting, either no AE used, or failure to follow AE specific regimen, or AE not strong enough.
The strongest AE's are prescription only, but still have source's on the web. The OTC AE's work for some, but not all.
Everybody who fails here, returns with no ill effects.
Sodium Nitr
ate will not kill you. It would take an enormous amount to be effective.
H2S, HCN, NH2Cl and Cl2 gases damage tissue on contact. Failure to ctb leaves severe damage behind.
SN does not damage tissue directly, rather it prevents the blood from properly absorbing oxygen to deliver to tissue.
Methylene Blue is a powerful antidote. It has allowed full recovery in all but the most severe (prolonged) cases.
Carbon-monoxide (CO) is also a popular method here.
It is more problematic than SN, and failure comes with some risks for long term damage.
If using, follow the method carefully.
I don't know anything about chloroform.