lumia 1520

pros
+latest specs (faster and most likely is upgradable to wp8.1)
+beautiful screen
+expandable storage

cons
-camera (image/video quality performs not as good as expected during low light/indoor. some say it is a fixable issue but since it is a 'hardware limitation', we can only hope for miracles)
-6 inch size (one hand operational is almost impossible.. unless u're a titan XP)
lumia 1020
pro
+camera (that 41mp speaks volume)

cons
-one year old specs
-no microsd slot (have to content with 25++gb but can relieve the storage burden with skydrive)
i was in the same dilemma as u r now but i've decided to wait for the next nokrosoft flagship instead because those 2 beasts of a phone above doesnt really convinced me to break the bank yet.

why not wait for 1 more week to see what nokcrosoft is going to unveil in the CES on 7 jan 2014? unless, u really need to buy the phone right now, i'd say go for the lumia 1520. only because it's the latest high-end lumia and upgradable to wp.8.1.