With most Android devices, you can unlock the bootloader and replace the Rom, root the device for administrator style access, debloat and remove system components, generally modify the hardware as you see fit.
With all Android devices that aren't managed (read: business device), you can sideload a third party app store without the need to use system exploits to 'jailbreak.'
Neither can be done on iOS. Attempting to modify the system or sideload apps on iOS requires using exploits that are security flaws and will likely be patched out in a future OS update.
If you already have an iDevice and can't replace it, you basically don't have any choice.