Depends on what cam/recording format you're talking about. On an HVX, you can get better 720 by shooting 1080 and downconverting, but that's because the HVX's 720p prefilters to 960x720. The HVX's 1080p prefilters from 1920 down to (coincidentally) 1280. So you can get a very nice 1280x720 out of HVX 1080p.
But native 720/60p is going to look much way huge hecka better than downconverted 1080/60i.
On an HDV camcorder there's no prefiltering going on in 720, so you'd get better 720p from native 720 than you would from downconverted 1080 (all other things being equal, which of course they never are).