As some have already noted, s shaped arms tend be higher mass designs. The choice of arm (mass being a key issue) is generally dictated by cartridge matching (compliance), so you're usually nudged toward the curved camp or the straight camp by your cartridge.
Beyond that, there are enough other issues at play (bearing design, adjustability, etc) that the issue is IMO low priority (beyond aesthetics).
Beyond that, there are enough other issues at play (bearing design, adjustability, etc) that the issue is IMO low priority (beyond aesthetics).