Unless you frequently travel on routes that have good award availability and typically $400+ fares, it's generally a much better idea to take a $300 bump voucher than a "free ticket" bump voucher for two reasons:
- The ticket you buy with the $300 bump voucher will earn miles; the "free ticket" won't.
- You can use the $300 toward any ticket on the airline issuing the voucher. The "free ticket" can usually only be used if there is standard award availability, making it far more restrictive.