The depth you are asking for is a little silly given there is a forum devoted to
this sort of discussion and this is not it.
As for the question. Volleyball. It gives you stats which makes you win faster. You don't have enough skills to need that much MP, leprechaun is ok in certain scenarios (so use it when needed), mozzie is not good - all it does is kill stuff, which you should be doing anyway, goat the same, potato blocks stuff, but can be avoided by using safer moxie, fairy - see leprechaun.
In BM you can get the volleyball quickly. In HC and SC you should already have it. However, you would
want to have all of them and seriously... come on. Why not use whichever one suited your goals at any particular time? I know 90% runs are great and all, but for first ascensions just experiment a bit!