My shimano 657s (good pedals for clipless beginners too) are excellent in this regard.
My eggbeaters/mallets were always inconsistant. If you tried to twist your heel inwards they wouldn't release. They seem to only release by twisting your heel outwards. This may be due to the limited amount of movement possible when you try to move your heel inward (crank arm or other structure blocking you). They are controlled by angular movement with the crank brothers, which means you HAVE to move them a certain amount of degrees before they unclip. The fact that the cleats wore down fast made them unpredictable too, sometimes they'd release when I didn't expect them, which leads to bloody knees from smacking the handlebars/controls.
The shimano pedals use a spring that controls the release, while the movement to release is somewhat similer, spring tension is more the deciding factor instead of angular movement, meaning you can "unclip" easier (or you can unclip in some situations that would be impossible with the CB pedals). Not to mention the fact that you can SET this spring tension, whereas you have no option with the crank brothers. Unclipping when you don't want to is just as bad as not being able to unclip, as it leads to lacerations and other bad things. The crank brother's mechanism also contributes to unwanted unclipping events when you slam the bottom of the pedal against a rock. It simply "opens" the top mechanism when you compress the bottom one (by hitting it on a rock).
The other thing is clipping in. If you haven't use clipless pedals you may think that unclipping is the hard part, but you'll get it down in no time. Practice and do NOT ride the hardest trails right away, you need to go somewhere with a soft field to practice unclipping. The thing is that it becomes natural and you get used to it. I unclip without concious thought. On the other hand, clipping back in can be difficult, and trying to ride in nasty technical sections without being clipped in is a recipe for a crash. Some beginners (to clipless) think that they should ride unclipped through technical sections, but that's simply asking to crash. You have to ride through any technical section with enough inertia to roll over the obstacles, and then being clipped in helps immensely with your balance and control, so you can keep rolling over those obstacles. It's much more likely to crash on flats. The guys riding DH or freeride bikes on flats are doing big big drops or jumps or riding on skinnies where they need to be able to jump off the bike if necessary. Realize that many people DH and freeride with clipless pedals, and in those technical rock garden sections you'll still get better control with clipless, due to a better interface.
So the real challenging part is clipping back in after stopping in a technical section or steep uphill section. The eggbeaters were "ok" in this regard, but the mallets required you to sort of "roll" your foot across the platform to engage the pedal mechanism, this was usually sucessfull, but sometimes my foot would go flying off the pedal because it didn't engage. With a shimano pedal you can put your foot squarely on the pedal and your foot will "find" the mechanism, requiring little additional effort. The mallets required extra effort to get clipped back in. In this regard though, a bigger platform-type clipless pedal is usually a good idea for inexperienced (to clipless) riders. Shimano 434s, 545s and 647s are good ideas in this regard. They are a little more stable and confidence inspiring than the smaller pedals.
I won't ever agree that the crank brother's pedals (eggbeater type mechanism that is found in all their pedals) are easier to unclip, they are quite a bit more inconsistant due to a few factors, and there is zero adjustability. They are light, but far from reliable in my experience (multiple breakages and failures). They do have a fairly "easy" exit in terms of force required, but as I said before, it's all about the angle, if you don't get to that angle you won't come out, and you can adjust the tension on other pedals anyhow.
