I believe it depends on several different factors, such as what is the ROA, onset, duration, and then more intiate variables, such as, what is the persons tolerance, what is the personality type, and what does the user wish to accomplish through his/her/her-he's experience.
Personally, I am a pretty shy person with a lot of anxiety and stress. I suffered from OCD since I was 10 years old, and managed to get it somewhat under control for a period of time with SSRI's (sertraline), though it came back through other similar anxiety disorders (BDD) at older ages. I've always basically wanted to feel like things were 'okay', or that I was 'secure'. I experimented (well actually abused) alchohol pretty heavily for a teenager, and then marijuana, but ultimately heroin provided the high I was looking for. It's fast acting (through pretty much all ROA, though I inject when I use it), long lasting, and it takes care of pretty much every sadness, fear, or pain that I can possibly experience. On top of that it does a really good job at allowing me to only remember the fun times, instead of the horrible, shamefull and painfully ones.
Other drugs like cocaine, amphetamines and cathinones are also very addicting. For me Cocaine has the strongest psychological effect on me-for instance, if I watch a video of someone shooting cocaine I'll either start to feel nauseous, or I'll have to run to the bathroom before I crap my pants. Out of all the drugs I've tried (with MDPV coming in as a close second), coke has the strongest reinforcement power. Im really greatful that I've never had an insane ammount of money, because once I start using this drug, I am not able to stop until I run out-no matter what kind of quantity I have bought. I should mention that I'm an Iv user across the board, so when I used cocaine it was allways intravenous, which is in my oppinion completely different and more fiendish than the insufflated ROA.
Basically IME, any drug that enters my system the fastest and gives me the biggest boost, is what I go for. So for opiates-heroin and oxymorphone, stimulants-cocaine and MDPV, benzo's-alprazolam, psychedellics-DMT.
Nowadays Im trying to ease up on my drug use for fear of health consequences, and for the fact that I want to actually move forward, and the needle has been holding me back. I try and stick with less addictive (relatively) substances, and it works out okay, but does it compare to my DOC's? No. Just like adderall is never gonna feel like a shot of meth, clonazepam is never going to do for me what heroin does, but it gets me through the day, and I have a much easier time taking or leaving it (though benzo dependency is one of the worst addictions of all-at least in the sense that the withdrawal can be fatal, can cause long lasting damage, and the post acute withdrawal is hell)