INJECTABLE OR ORALS?
INJECTABLE -- human grade is safer and should only be used when possible.
So, testosterone, de_ca and pri_mo is available and should only be used when possible. Winstrol - stanozolol (injectable) Zambon is available and should only be used when possible (although we now know it can be taken orally which reduces the risks when using underground).
But, trenbolone, masteron/permastril (dromostanolone) are no longer available in human grade which means you have no choice but to go UG. So, if you are going to take trenbolone, or mast, go with the UG you trust. N_PP - - is available in human grade but not readily, especially not in concentrated dose (I think 25mg/ml is most readily available human grade which is low compared to UG labs which are dosed 100mg/ml or higher).
ORALS -- human grade or underground not as important. The gastrointestinal tract will filter out any impurities. Unless it contains bacteria/virus/poison, the human gut can withstand most impurities without much risk to health. Think of street drugs, fast food, processed foods, that no one knows how sterile the conditions were when they were prepared. Nonetheless, we hear very little about health concerns regarding impurities from oral ingestion of foods or street drugs (pills). The risk is taking something intramuscularly (i.e., injectables not orals) that goes directly into bloodstream and is not filtered through the gut. Your body usually knows how to get rid of impurities taken orally that it cannot digest/withstand -- PUKE!
ALSO, you have no choice but to go with UG for most orals other than Dianabol - methandrostenolone - and Anadrol -oxymetholone - . Actually, the only Dianabol - methandrostenolone - not UG are naposims, unless you can find Russian. Usually ppl go with ********

or various other UGs. But high milligram Winstrol - stanozolol is not available human grade (2mg/pill is not cost effective), neither is anavar (albeit BTG which is nearly impossible to get hold of), Turanabol.
So you have Dianabol - methandrostenolone - (naposims), Anadrol -oxymetholone - (Anapolon, Iranian), halo, proviron (not really an anabolic, really an androgen), and low dose Winstrol - stanozolol. You almost have to go with UG if you want to use Anavar - oxandrolone - , Turanabol, Winstrol - stanozolol. (and even Dianabol - methandrostenolone - -- snake and arrow are ug, blue hearts are ug, most Dianabol - methandrostenolone - is ug).