All four of them are "absolutely wonderful" sororities. So are the other 22 NPC sororities.
Are there tiers? Yes. Are some NPC sororities stronger than others in certain regions? Yes. Do some sororities have larger numbers of chapters and initiated sisters than others? Of course. What's important is for each PNM to see beyond the tiers and the stereotypes and to pursue the sorority/ies she feels a connection with. If that's a "top-tier" sorority with 500 chapters and a million sisters, so be it. If it's a smaller sorority with "only" 100 chapters and 100,000 sisters, so be it.
</soapbox>
So, where's the update already??