I'm not sure soft start has any great advantage: my cheap (powerjack) inverter as such a slow soft start that it stalls the freezer motor. But in practice I wouldn't start the inverter with the whole house connected anyway because if the power's been off for a while all the freezers/fridge/dehumidifier would be trying to start up simultaneously. Much better to start the inverter then connect the heavy startup loads individually once it's up & running.
I suspect most pure sine inverters are soft start anyway, wether you want it or not. If it were me I'd focus more on the other parameters of the inverters you're looking at.
If you prefer to start it with loads on; then consider what sorts of loads they are and how they'll react to it. As Damon says resistive loads, and probably most small electronic loads (LED lights for e.g.) will be fine; computers: not sure.