For a while, there was an orbital calculator out that suggested going towards a heading of 180 for inferior planets. I'm not exactly sure why, but everyone just assumed that was the way to do things. Launching towards 90 gives you some extra DV, but it's only about 175m/s iirc, so it wouldn't be the worst thing in the world to launch to 180, but there really isn't any benefit. I've heard of some countries here on earth launching towards the west, but that's only to avoid flying over enemy territory or no-fly zones. The only reason I can remember doing it in game was because I wanted to rendezvous with a target that was already orbiting in that direction. You'll be fine always launching to 90, the only thing that should change from superior to inferior planets is your escape angle. My rule is always to burn at sunset for superior planets like Duna, and sunrise for inferior planets like Eve. It seems to get me close enough.