Personally I think that it has a lot to do with what your local metagame looks like. For example if in your area if you have a lot of players that play terminator heavy lists, daemons, DE, and now GK null zone might be a better choice for a power. Why? because all those types of list have a high number of units/models that can take advantage of invul saves so null zone becomes much more potent. Now if most of the players in your play horde armies, or armies that don't have access to a large number of invul saves then going with gate of infinity would be a much better choice because it will give you more mobility options.
Like I said I think that when building an all comers list you really do have to take into account your local metagame and what exactly you will be facing. For example, I play SW and in my area most armies that I face off against are SM of all varieties, IG, DE, and now GK. So when I pick my powers for my Rune Priest in my all comers list I keep that in mind and take the two powers that would be most useful for me which is useally living lightening and murderous hurricane. Now if I was going to play in 'ard Boyz or a GT I might take different powers like JotWW or some of the other more situational powers because of the odds of facing armies that I don't normally face off against.
So I guess the long and short of it is, there really is no better or worst power it's all situational, and how best will it fit into your list and help you do what you want to do.
Good luck and happy hunting,
Arkreaver