Technically speaking--->
10mg of diazepam (Valium) = 2 mg lorazepam (Ativan) = 1mg alprazolam (Xanax). I'm assuming you already knew that though, and are asking which ones different BL's prefer. Here's what I know about the three benzos----->
-All three are wonderful anxiolytics, sedatives, and muscle relaxers.
-Ativan and Valium are both used clinically as sedatives and muscle relaxers while Xanax generally is not...probably b/c Xanax is a more powerful (and thus technically more dangerous) sedative.
-Xanax nad Ativan are more powerful sedatives and hypnotics than Valium.
-Valium has a quicker onset and shorter duration of action compared to the other two.
-Valium has less rebound symptoms, as in hangover symptoms that one might experience after coming down. The hangover may occur the same day of the dose or the next day after a night of benzing. Common hangover symptoms are drowsiness, feeling like crap, feeling depressed, and increased susceptibility to anxiety (aka rebound anxiety).
-Ativan and Xanax are better for patients with liver problems because they are easier metabolized.
I'd rather take the Xanax because it's a more intensely sedated feeling. Valium is great for things like public speaking, because you need high doses to become sedated. At the right dose, Valium takes away all anxiety whatsoever without making you feel sorta drunk. Xanax is better for gettting fucked up, which is generally my goal with benzos. I used to take Valium a lot in highschool, because it helped immensely with my classroom anxiety. I was able to give the right answer, make the entire class crack-up, and side-track the teacher into talking about something that was actually interesting. I can do stuff like that without Valium now that I'm in college, a more comfortable setting for me. Xanax is great for sinking into the couch and having a blast watching some otherwise mind-numbing TV show or playing some video game that I would get bored with quickly without the drug. Ativan is less intense than Xanax, but seems to be longer-acting.
I need much higher doses than those listed in the OP, though.
Valium is better if you're planning on taking a benzo for an extended amount of time (x days in a row). It is common knowledge that the withdrawal from Valium would be easier than that of Xanax/Ativan if all three drugs were taken in similar doses by similar people/body types and for the same amount of days. I don't know that personally because I avoid benzo w/d at all costs. I don't want to be having a seizure any time soon.