Choose Hard if it's CHF 150 cheaper per month, the commute to HB is 5 min shorter — more central and connected, there's a denser restaurant scene.
Choose Wollishofen if it's noticeably quieter (48 vs 60 dB), it scores higher on safety (8.5 vs 6/10), it has better green-space access (7.5 vs 3.5/10).