I have both on mine... KAC BulletFlight and Ballistic FTE (Field Tactical Edition).
If you want to play 'what if' and while away the time in the carpool to work or in the elevator or in a meeting
Ballistic has lots more options for graphing and comparing multiple loads. If you want something that you can do a paperless range log in, Ballistic works great for that too. The interface for getting a load into the HUD (heads up display) w/ the rollers is a bit of a bother, though. Not hard, but the very last step for saving the name of the load has gone awry on me more than once, and then its start all frickin' over again... depending on the level of customization/tweaking you did, that might be more or less frustrating.
Bulletflight has far fewer options. You save things by rifle, not by load. If you use two loads in one gun, you'll have to save things accordingly. It's more stream lined in operation - for me. Open it up, select a rifle/load, hit 'Calculate Simple' and you're off and rocking w/ the HUD and the rollers. This assumes a certain amount of 'pre-adjusting' the applicable parameters like environmental conditions, etc.
Overall... for just shooting the one I keep coming back to is BulletFlight.
YMMV,
Monte