The experience of doing it with a password is pretty poor compared to using a TPM. Every time the computer reboots, I need to type in the password. If it is a remote machine, I have to physically be at the station to type in the password.
Keeping the key file on a USB drive isn't exactly safe either, as there's a high likelihood that flash drive is probably going to be near my computer when stolen. Also, that flash drive may be active and plugged when the system is running, exposing it to the machine directly. Having that key material easily accessible on a flash drive makes it less protected than using the TPM.
Using the TPM gives me a better experience and depending on how things are handled a far more secure way of handling the key. Its way easier to grab the key file off the flash drive than coaxing it out of the TPM without booting the trusted boot process.
Keeping the key file on a USB drive isn't exactly safe either, as there's a high likelihood that flash drive is probably going to be near my computer when stolen. Also, that flash drive may be active and plugged when the system is running, exposing it to the machine directly. Having that key material easily accessible on a flash drive makes it less protected than using the TPM.
Using the TPM gives me a better experience and depending on how things are handled a far more secure way of handling the key. Its way easier to grab the key file off the flash drive than coaxing it out of the TPM without booting the trusted boot process.