That's kind of a toughy and depends on your priorities/needs, both are similar in many respects yet differ in other ways. If you can, go to
GSMArena.com - GSM phone reviews, news, opinions, votes, manuals and more... and do a comparison between the two, that might help with your decision making.
Some of the main differences (730/830)...
Display Size: 4.7 vs 5"
Display Type: OLED vs IPS
Internal Memory: 8 GB vs 16 GB
Primary Camera: 6.7 MP vs 10.0 MP w/latter having OIS
Secondary Camera: 5.0 MP vs 0.9 MP
Actually own the 830 and the rear camera is nice especially with it having optical image stabilization. The 5" in display size is my sweet-spot, and although the IPS display resolutions isn't spectacular (not terrible either) after seeing the OLED display we definitely prefer it over IPS. Both have expandable storage yet my preference for internal is "more the merrier", so 830 gets the nod with its 16 GB of internal storage.
All the best in your ventures :smile:
PS... If you are on a budget and the 650 is available in your area for a reasonable price I'd opt for it, very nice phone with a decent rear camera (8.0 MP) and it too has 16 GB of internal storage, expandable as well.