It doesn't make a difference which one you use. Lily pipes are transparent and thus they are more natural, it's all for aesthetics. Lily pipes are similar to the Fluval outflows, but of course more elegant. Spraybars give a more even flow throughout the tank, while lily pipes give a stream-line current. Again, it's all down to aesthetics..which of course comes at a cost.
The best position is to point the spraybar 45 degrees downwards, this is to reduce agitation which dissipates C02. As for the lily pipe, there's only one way to place it.