Well i say, if you have the money and want a more reliable setup, go for the direct porting. I have a 100hp shot ported through my manifold and apart from the lines getting blocked (due to lack of purging) i have had no probs with my Nos. The timing on my engine has been changed, but nothing else has been touched.
With the direct port system, it distributes the nos and fuel into each intake port on your engine, which makes it extremely powerful and just as accurate. The power is coming from your fuel itself as your engine is getting supplied additonal fuel, so you also need to make sure your fuel system can keep up with the extra amounts of fuel going through it, if it can't you will need to change this, otherwise there is no point in having nitrous put through because it won't make a difference.
Also if you go ported, make sure the person doing it knows what he is doing as this is the most difficult kind of Nos setup as you are acutally having to drill into the engine area.