They both have 5 ports, so either one will work. You may want to figure out what kind of throughput you're expecting, and compare the throughput tests for both devices on routerboard.com.
Personally I'd also advocate the 450 because it has a serial port, which is awesome when you screw something up and need a local console to get back into the router.
functionally they are both identical, as fewi says. the differences are the case, the serial port, the RouterOS license level (only matters if you will have more than 200 active users)