For me, I am staying with my Lumia 920 until (hopefully...) the flagship Windows phone drops for Windows 10. I am hoping it'll be a 4.7 to 5 inch screen, Qi wireless charging, pretty good camera (doesn't have to be as good as 1020's 41MP), Glance screen, good battery life, "Hey Cortana" - ya' know, the true upgrade to the 920. My 920 is still plugging along nicely on AT&T's network and haven't really experienced any issues that others are having (battery life has dwindled, but I always have chargers near by so not a big deal for me).
The 1520 is too large for me. I've played around with it in an AT&T store and ... the size just wasn't for me. While the 830 is a good phone and has good specs for a middle-of-the-road phone, I am not ashamed to say I want the best that Microsoft can give me. Despite WP 8 and Windows 10 not needing the cutting-edge hardware, I feel better knowing that my 920 still has better specs than 3 out of 5 smart phones in people's hands. Having higher specs means I am more likely (not always though, aka "Hey Cortana") to receive and benefit from future software updates - ensuring I get more out of my phone.
Sorry for the long post and I think I reiterated what a lot of people were thinking, but just wanted to give one more opinion on the subject in case Microsoft employees are looking at this thread.