I've been going Thor crazy after having been knocked out by The Dark World (already one of my favorite Marvel live actions). I first read Thor back when the might John Buscema was doing the pencils. My ranking:
1) Simonson
2) Conway/J. Buscema
3) Lee/Kirby
4) Aaron
5) Straczynski
The little I've read of the Fraction was okay, but I don't put him up in the above realms. The art of J. Buscema made up for some of Conway's weaker writing (which admittedly occurred more than rarely).