Should the AC-Live or AC-Neutral wire be 'broken' by a relay?
Surely this is specified in whatever electrical code applies to your jurisdiction.

Put the switch in the hot line, not the neutral.

Even without the electrical code, a few seconds thought should have revealed the answer too.  Purely from the device's point of view, it doesn't matter since the device and switch are in series.  The switch in the neutral line will work correctly.

However, consider the voltage the device will be at in both cases.  With the hot line open, the whole device is at the neutral potential.  With the neutral line open, the whole device is at line potential.  This isn't supposed to matter, but stuff happens.  With a lot of moisture around, for example, external surfaces could be connected to line voltage thru the moisture leakage path when the neutral line is open but the hot line not.

In cases where there are two hot lines going to a device, like 240 V devices in the US, you should be switching both of them.  There are ganged switches (DPST) just for this purpose.  This doesn't apply to something low power like a bathroom light and fan.  I only mention it for completeness and to better illustrate the point.