- Apple: next...
- Samsung: supports unlocking the bootloader (enable developer options, enable OEM unlock, boot into download mode and follow the on-screen instructions for "Unlock Bootloader")
- LG: supports unlocking the bootloader (see http://developer.lge.com/resource/mobile/RetrieveBootloader....)
- Lenovo: supports unlocking the bootloader (see https://www.zui.com/iunlock)
- Motorola: supports unlocking the bootloader (see http://motorola-global-portal.custhelp.com/app/standalone/bo...)
In other words, all devices in your list support unlocking the bootloader.
I've used devices from many different manufacturers from around 2010 onwards, none of them run vendor distributions. It used to be difficult to install new distributions but this has not been the case for more recent devices. I'm in Europe but often source devices from elsewhere since they are not 'officially' sold here.