Ah right, then fair enough, sorry, that's just been irritating me for quite a while, now I can give a decent answer.
Simply enough, Nelo Angelo is stronger, can teleport and has a lot more going for him, but Alastor can also fly and rain down lightning upon Nelo, something that he can do very little about other than fire inaccurate fireballs back at him.
In short, just due to the fact that Alastor can throw down lightning and fly much faster than Nelo can move, plus Nelo can barely counter attack that, I believe Alastor easily has the upper hand.