I probably wouldn't suggest the dagger of distortion; it's really, really risky to unwield it (Unless your character can reliable get out of the abyss and has enough HP to survive the other miscast effects.).
Distortion does alright damage, and has a chance to 'insta-kill' (well, banish to the abyss, which is basically th'same thing, except that you don't get XP for it.), but later in the game a stabber (if that's what you are) will want to switch over to some other short blade, probably either a sabre or quick blade; the raw bonus damage from stabbing (which daggers double) caps off at some point or another, after which you probably want whatever has the higher base damage. There's a number of reasons to want to be able to easily switch out weapons, anyway -- use ID, rods/staves, sublimation of blood, cards, etc, etc.
I'd probably say use the venom dagger on things you can kite with it, and the stabbing one on everything else... and keep an eye out for Nikola, who has a guaranteed sabre of electrocution (My SpEn's currently using it as his primary weapon, despite also having a quickblade of freezing.), providing you can kill him. Keep an eye out for the lesser elemental and draining/pain brands, in the mean time. Protection's also very nice. But distortion, chaos, and vampiricism for anything-not-a-deep-dwarf is generally a raw deal. Speed's nice for everything not-a-shortblade. S'not a bad idea to keep a holy wrath weapon around, just in case.