The 431.0-433.0 MHz and 435.0-438.0 MHz segments are a NO-NO by FCC law for FM. (Part 97, subpart 39[b]) Stay out of those areas. 420-432 and 438-442 is used for amateur television, so that's no good either.
Ideally, you would want to be somewhere between 442.025 and 446.075 on an .025MHz step. Just listen first, research the repeaters in your area to make sure you are not close in frequency to any of them, and you'll be fine. For instance, for my cross-band at home, I use 443.325, with a DCS tone to keep others out. It crosses to my local 146.820 VHF machine about 20 miles away.
Keep in mind that the national simplex calling frequency for 70cm FM is 446.000, so you'll want to stay clear of that also.