Here some background.
I do not have a 1520 but a 820, 925 and 930 and the dt-900, dt910, dt 601.
The DT 901 is actual a DT 900 in a "bag".
I would not recommend the dt 601 because it "too small" even for a 930 in my opinion.
I like the dt 910 the most because it is also a stand.
For charging "speed" there is no difference between the 900, 901 and 910 because they all have 750 mA input current and the dt 601 has 1700mA and the DT 903 has 2500 mA.
So the fastest would be the 903 which is also the most "fancy" one with LED and NFC (910 also has NFC).
But because QI charging is "easy" I do not think charging speed is that important because it's easy to put it on the charger.
Price wise the 903 will be the most expensive.