This really is a question with no correct answer that we can offer you. Both cameras have their pros and cons, so it really depends on what matters to you.
Having said that, I started with a 20D (which is essentially the same as a 30D) then upgraded to a 5D. I find that the 5D is a more pleasurable camera to use and in most situations is the better camera for the job, because of that lovely FF sensor. However the 20D is still used as a second body, when I am at an event and don't want to have to keep swapping lenses, it is also my camera of choice when shooting action or birding etc.
So, usually I use the 5D but at times I prefer the 20D, particularly when I need the 5fps frame rate or extra reach. Incidentally the extra reach is not because of the 1.6x crop factor (you could simply use PS to crop the 5D image to match, if that was the case), it is because it has smaller pixels and so more will be covered by a subject of a given size - so the subject is larger in pixel terms. The difference in reach isn't as great as you might think, one of these days I am going to do a comparison test to see just how much difference there actually is.
Which is the better camera ? The 5D, definitely.
Which is best for you ?? Only you can decide, it depends on your needs.