Depends what you mean by "better". All these things are simply different tools for different jobs. Every reverb has a different character from every other, and it's then a matter of deciding which has the right character for the job in hand. There's no implicit difference between standalone processors and PC based processors (they are both programs controlling chips which do the number crunching).
One factor to bear in mind is that if the outboard effect is being used to process the audio before it is recorded, then you're stuck with the effect on the recording. If you do the processing afterwards with Audition or whatever, you can change your mind as often as you like. If you do the processing afterwards using an outboard effect, you may lose quality in getting the audio out of your PC and into the outboard and back, depending on exactly how you do it.
Consider for instance Audition's limiter. It can be easily shown that it passes the audio through bit-for-bit unchanged except at the points where limiting is required. As soon as the peak has passed, there is absolutely no change to the original audio. Using an outboard effect, that might not necessarily be the case, and in any event you'd have a harder job to prove it.