Choose Wipkingen if it's CHF 250 cheaper per month, the commute to HB is 3 min shorter — more central and connected.
Choose Wollishofen if it's noticeably quieter (48 vs 52 dB), it scores higher on safety (8.5 vs 7.5/10), it has better green-space access (7.5 vs 5.5/10).