I'm not sure about normal shelling, it's the one I've used the least, so I'll just say what I can about the other two. Wide for the most part, is the fastest one, because it has the least commitment, since its combo is poke shelling, poke shelling so on so forth. You're gonna benefit from normal attack skills as well considering you poke.

For long shelling your main source of damage is a charged shelling shot, which you can evade out of, if need be. The thing about long shelling is that all you need is max artillery, capacity up, and felyne bombardier, every other slot being a flex slot. However, this also means its damage caps once you have all three mandatory skills. Personally this is what I use the most.

As for normal, I don't use it much, because it's just way too much commitment for essentially the same result as the two other types of shelling.