Stronger opioids such as heroin, fentanyl, or oxycodone are generally preferable as other types of opioids require much larger doses and thus have higher risk of failure. For example, heroin is about 10x as strong as morphine.
Pharmaceutical-grade opioids might be considered preferable by some given that their dosages are accurately labelled and they are not potentially contaminated or sold as different drugs entirely like with illegal markets. However, many pharmaceutical opioids also contain high concentrations of anti-inflammatory drugs such as paracetamol, acetaminophen, or ibuprofen (e.g., Percocet) that are likely to cause significant stomach pain and damage organs in the doses required to ctb. They also often contain fillers (e.g., Oxycontin) that make them unsuitable for injection or other routes of administration. Eating these medications is also not recommended as it is very likely to fail due to vomiting and oral bioavailability is low.