I have played in Amber diceless and ran a Vampire TM game that was more often than not diceless (not really intentionally but when my players stopped bringing mtheir dice to the game I realized how much narrative resolution we were doing.)
In the hands of a bad Dm, neither diced nor diceless will work well at all. A Gm can make any encounter as unpredictable or predictable as he wants well before the players even arrive.
Diceless is not for everybody. It requires a GOOD GM and experienced players. The group has to be very much into a collaborative game and not a competitive game. If you want to show up an "game against the GM" diceless is NOT for you. If you think your GM 's decisions are arbitrary, predictable, or unimaginative, stick with diced.
On the other hand, if you want the outcome to be unpredictable but determined by choices you make (when positioned against choices they make) and want your efforts and decisions reflected... diceless is for you.
If you want to see your character fail for a REASON in game, and not because you rolled poorly, then diceless is for you.
If you feel that the proper order is to determine why your character SHOULD fail and then decide whether he did, as opposed to determine whether he failed and then start trying to explain why he did, then diceless is for you.
Speaking for the amber system, it takes the uneducated die roll, where the 1-20 swing has nothing to do with your actions, decisions or scene drama, and replaces it with double-blind partially informed decisions of opposed actions. Its that same double-blind partially informed methodology that adds the random element into any diceless competitive game such as GO or CHESS and produces a variable outcome even though the levels of player ability may differ.
There is randomness in diceless resolution, its just not based on arbitrary.