This is how I view 1-4 stock matches, personally (no time limits);
One Stock - Accidents can end the game, no cushion for comebacks.
Two Stock - Even with an accident, or some mishap, you're still in the game. But, your opponent has a cushion that you do not. Each percentage of damage you take is something you can't afford to take, and something your opponent can.
Three Stock - Personally, it provides a balance. There's a nice cushion for a comeback should you die first, or if an accident happens. This doesn't give your opponent a terrible advantage, since you still have room to maneuver without losing immediately.
Four Stock - Same advantages like Three, but I feel this drags out games too long. This can also provide your opponent with a considerable lead should you take too much damage after your first death.
Overall, Three Stock provides a nice balance of speed, cushion for comeback, and less advantages for the leading opponent. This is my opinion, but I tend to play Three stock more than anything else.