Shooting on the HVX. Have shot tv before but wondered if there was a better format than another for cross conversion of 720 and 1080i.

Cross-converting between formats has little to do with the codec shot and more about the quality of the original footage. Many have upressed HVX 720p into 1080 with good results but this too has a lot to do with the methodology and applications used.

If you're doing broadcast TV then the most important thing is knowing what the network wants; you'll need to give them a test file and see if your finals pass their QC standards.