Hmmm, I thought this question was very subjective. Being an opiate abuser and having tried like only six of seven benzos regularly, I never found them recreational or euphoric.
Anyway, while researching nimetazepam, I found this on wikipedia:
"Together with temazepam abusers, they accounted for 47% of the abusers arrested in 2005.[4] In Japan, where seizures of diverted nimetazepam are mostly concentrated, it remains as a major drug of abuse... Japanese organized crime syndicates control the distribution of nimetazepam and to a lesser extent, flutoprazepam, temazepam, midazolam, and triazolam, all of which are the most heavily controlled and most in demand benzodiazepines throughout East Asia and Southeast Asia.[5]
Darke, Ross & Hall found that nimetazepam was rated extremely high by drug abusers, rating second only to temazepam among benzodiazepines. The two most common reasons for this preference were that it was the ‘strongest’ and that it gave a good ‘high.'
So according to Darke, Ross, and Hall (whoever these guys are):
1. nimetazepam
and
2, 3, 4, 5: flutoprazepam, temazepam, midazolam, and triazolam
I think it may have to do with water solubility for injection (except I know triazolam (Halcion) isn't very water soluable, but is pretty good when IV'ed with <10% of alcohol, don't do it).