Palm, Android and Blackberry are light years ahead of Apples app standby or faux multi tasking. No one here can honestly say that Apples its the best.
How Apple could possibly be in the lead with their half baked multitasking compared to Palm is beyond me. I am a dyed in the wool iPhone user and won't be getting a Palm any time soon, but you'd have to be blind not to see that their multitasking UI owns the iphone's.
I think that iOS and WebOS have two fundamentally different implementations. I don't think it's appropriate to say one is better than they other as they both have their strengths, although certainly a person may prefer one or the other.
In the classic approach to multitasking, users consciously open and close apps; only open apps are shown in the multitasking UI. The advantage of this system is that it has real power in organizing a user's train-of-thought, preserving work flow, and keeping context. When using an app, the user follows a particular train-of-thought of what they are doing in the app. They can "hold that thought" when switching to another app. The multitasking UI acts as a cue to their minds to resume the thought processes associated with each open app. When the user closes an app, that train-of-thought is complete and our mind no longer has to keep track of it.
Out of this system, WebOS is easily the best-in-class. The card system easily manages open applications in a way that leaves no ambiguity for the user as to what is open or not. Closing apps by flicking away the card works beautifully as well. Finally, there are no limitations because apps are fully functional in the background.
In Apple's multitasking, users do not consciously close apps; all recently used apps are shown in the multitasking UI. While it isn't perhaps as organized as the classic implementation, it makes up for it in speed and usability.
There's this "fire and forget" mentality without having to consciously close apps that makes jumping in and out of apps very quick. It requires less mental energy because the OS handles closing/opening (re-opening) apps, not the user. The fast app switching is essential and the snazzy animation completes the illusion. The most-recently used app multitasking bar is faster at switching apps than the card system of WebOS.
Finally, while background processing is limited to certain set of APIs on the iPhone, it is also flexible; Apple can add multitasking APIs to extend functionality.
I was one that was hoping that they would flat out rip-off the scheme from WebOS, but after using multitasking on the iPhone, I quite enjoy it. My only complaint so far is how the multitasking bar is a UI patch-job; it feels like more of an after-thought than really integrated into the OS. In principle, it's disappointing. In practice, however, its quick to summon, the animation is fluid, and it gets the job done.