Pretty sure the 'official' equivalency is 10mg diazepam - 1mg alprazolam. Plus, from experience, I find 10mg valium much stronger than 1mg xanax. But each hit different sub-receptors. Xanax is best for anxiety of a mental kind, valium is nice and relaxing both physically and mentally and more akin to something recreational. I find xanax 100% medicinal, no idea how people get 'high' off it. Just makes my gut pain stop and my agoraphobia stop.
I think it's opposite. YMMV, but xanax is great for me and my doctor agrees because it never makes me sleepy. Diazepam/Valium tends to leave me too tired to drive, whereas I can be on a bar worth of xanax and 100% awake.
I want to emphasize that all BZDs affect people differently. For me, xanax is purely medicinal, klonopin holds no value whatsoever until I hit high dosages, and valium hits me in all the right places both relaxation wise as well as medicinally but can be too sedating. But xanax is unique for me in that it 100% eliminates my gut pain when I have it bad. Other bzds don't. Go figure. I also require higher doses in general for bzds. 0.25mg xanax puts my wife to sleep while I can be out and about, life of the party on 2mg