Depends. 830 is a newer generation device, so its got newer gen specs that support stuff like SensorCore (think fitbit), will support voice-activated cortana when that comes out, etc. Because its a quad core you’ll likely not run into “Resuming…” screens to much and you performance when taking pictures should be snappier. The Battery life is also much likelier to last longer because its a bigger battery on top of the processor being more efficient.
That said, the 1020 is not slow at all. You might hit “Resuming…” screens when loading up heavy hitter (or poorly optimized) apps but its not a big deal at all and never takes long. The entire OS runs pretty silky smooth all the way through. The screen is (IMO) much better and supports features like Glance. The camera is top of its class – there isn’t a smartphone on earth that has a better camera. The biggest downside is the battery life sucks when using intensive apps (especially camera and stuff like Readit), so you better have a portable battery charger on you. The other downside is the shot-to-shot times are slow. It takes about 3 seconds between shots due to how big the pictures in the camera are. Its definitely a phone you use if you want to take calculated and amazing pictures over quick selfies.
Personally, if you aren’t interested in the camera and don’t mind a slightly worse/average-but-still-much-better-than-a-520 screen, the 830 is more current and likely better for everyday smartphone usage. If you are interested in the camera and having a better screen that supports glance, you won’t feel like you are compromising by getting the 1020. Especially since, at this point, the 1020 is undoubtedly cheaper than the 830 (I got mine for $310 including camera case which I sold for $45).
Speed wise they are both pretty comparable. You aren’t going to run into performance issues with these phones. The 1020’s speed disadvantage lies in shot to shot times with the camera and you will likely run into more (very brief) “Resuming…” screens that last maybe a couple of seconds at most compared to the 830.