Look here, "best" is highly subjective.
Best for me is not the best for many other people.
It is highly dependent on what you value, as I've said in other places.
Low price? The 1520 could be the worst.
Photography chops? 1020 is king.
etc.
etc.
The 1520 and 930 are about the same under the hood. (they have the same specifications)
Physically, the 1520 is much larger than the 930, but also has a different design.
The 930 has a metal border with a "pillowed" plastic back. The 1520 is more, well, you can see from photos.
The size is a big sticking point for me, but many enjoy phones like the 1520 and Galaxy Note.
You're looking at a 6" IPS LCD screen vs. a 5" AMOLED screen. Both are at 1080p.
Which screen tech is better? that's subjective, but they are definitely different.
worth noting that the 1520 has "Glance" a seemingly insignificant feature, but one that many, including me, value highly.
the 1520 has a microSD card slot, which the 930 does not have. Both have 32 GB of storage and Qi wireless charging. (except in the case of the AT&T 1520 in the USA, which mainly has 16 GB, there is a 32 GB model, and no Qi.)
The battery in the 1520 is larger, and life is superior.
The 930 might have SensorCore, which IIRC isn't in the 1520?
Not something I care about though, but someone else might.
Those are most of the differences at least, I feel I've missed some spots.
No flagship on the horizon.
EDIT: actually, you may want to read this:
http://forums.windowscentral.com/nokia-lumia-930/324660-just-grabbed-930-a.html