If the doses were even, I'd pick diazepam, hands down. Good for all your "therapeutic" purposes, but also more euphoric and "warm" than the others.
However in reality Valium is rarely dosed on an equal basis, so my practical choice would be clonazepam. When I was drowning in euphoric benzos, I didn't appreciate it very much. But now I find clonazepam wonderful for practical purposes, sedating and muscle relaxing but still manageable, not to mention its unbeatable legs (buta decently quick onset, especially sublingual IME).
Alprazolam I found useful for how quickly it kicked in and its ability to be used as a borderline sleeper. The hard-hitting effect had a certain euphoria, but I found it kind of "cold" and not to my personal taste (though I wouldn't kick it out of bed, that's for sure).