I don't know which one I should choose: lumia 630 ' 720 or galaxy s4 mini.
What I find important:
1. Privacy
Say what you will about Google and Microsoft, but its not an easy question. Ignoring the services attached to the devices, both OSes can be secure from the average joe, you have options on both sides. Because of the freedom given by Android, malware is a possibility but currently not a likelihood just yet if you exercise common sense.
2. Speed
The Lumia 630 might have a slight edge over the 720, but I hold it as negligible.
The S4 Mini is more powerful, and Android will likely work, however Samsung's additional bloat can potentially bog down the device. Performance can be improved, it will likely be workable. I can't say since I don't have firsthand experience. (except with a HTC Aria, which was usable with 800 Mhz single core, 384 MB RAM) It likely won't be the laggy disaster many like to call Android.
3. Screen
The 630 has the worst display, but the largest. Then the 720, then the S4 Mini. However, the Lumia 720 (dont know about the other two) has super sensitive touch. Both Lumia's have a sunlight readability mode I dont think I've seen elsewhere.
The S4 Mini's is sharper and probably the same size as the 720's. The display tech is different too.
4. Battery life
I expect the 720 to be the best, followed by the other two. The 630 and S4 mini benefit from a replaceable battery.
5. Camera
The 720's performance in low light is relatively good, the 630's is the worst overall camera, the S4 mini likely slots in either better or worse than the 720's. I don't know firsthand.
Can you guys please help me?