Separate outlets means running cable that you won't use most of the time, and having to remember which outlets go to which circuit.
A transfer switch allows you to isolate and switch between two power supplies so that your house circuits are only ever connected to one of them, and the two supplies are never in the same circuit[1]. They can be had for a few hundred depending on the load[2].
[1] this is a break-before-make switch. There exist make-before-break switches for when you need uninterrupted power supply, but they're not appropriate for this case as you'd be backfeeding into the grid which is dangerous and illegal.
A transfer switch allows you to isolate and switch between two power supplies so that your house circuits are only ever connected to one of them, and the two supplies are never in the same circuit[1]. They can be had for a few hundred depending on the load[2].
[1] this is a break-before-make switch. There exist make-before-break switches for when you need uninterrupted power supply, but they're not appropriate for this case as you'd be backfeeding into the grid which is dangerous and illegal.
[2] https://www.lowes.com/pl/Generator-transfer-switch-kits-Gene...