Choose Alt-Wiedikon if it's noticeably quieter (52 vs 68 dB), it scores higher on safety (7.5 vs 5/10), it has better green-space access (6 vs 2.5/10).
Choose Langstrasse if it's CHF 200 cheaper per month, the commute to HB is 5 min shorter — more central and connected, there's a denser restaurant scene.