which is better visability wise?

if you go on the floor you can usually see zero -except the big screens.
the lower sections have good visibility - if you're higher up. the balcony is fine -you just get nose bleeds:D

When you say stalls or balcony, I take it you mean floor area or tiered area. My opinion is really it depends which parts of the floor you can get, what the show is etc. If you are taking children the floor is all one level so you can get visibilty issues but if you are nearer the front there you can get nearer the stage. Of course this is sometimes just a standing area for some concerts which is also good for moshing.

Obviously on the tiered area you are a bit further away but the blocks nearer the stage give a good overall view. The blocks starting with 1 are the lower tier and IMO give a better view than the higher tier. I usually avoid any of the blocks that are at the rear of the arena as I think you cant see very much at all from there.

I take it the balcony is no good for those scared of heights then, oooh a chance to be evil :P

In my opinion, I think the floor is ok if you're within the first section, so about 20 rows back I think. But it depends if you're short or have kids! Then the next best is the 1st tier, with the first couple of blocks nearest to the stage being best. I was in the block nearest to the stage on the first tier the other week for McFly and it was a great view.

I guess it also depends what you are going to see...for example ice hockey, i prefer the back of the lower tier rather than up in the nosebleed seats but for concerts I have found the floor to be fine.

Wherever you choose, don't go for the back section furthest from the stage. Absolutely awfull! The side seats on the first tier are pretty good.