It is plain that lifting gives the opposing man a large variety of shots that can be hit for winners - that is why I believe the mixed battle is won or lost with low or net shots. I keep one foot near the center line. This is essentially the defensive formation in classic mixed doubles, with the woman close to the short service line but cross-court away from the opposing shuttle, and the man to one side of the center line on the same side of the court the shuttle is on. Given this formation, if the man must lift, it is safest to lift straight, so that his partner would be closer to her cross-court defensive position. Likewise, if the woman must lift, it is safest for her to lift cross-court so that all she has to do is take a step backward to defend.
Many mixed teams defend side by side like regular doubles.
Ultimately the best defense is a style of play that precludes lifting to the back. The quicker one gets to the shuttle the better, because it is harder to hit a successful net shot or half-court when the shuttle is near the floor. Unless the opposing man is slow-footed, drives are usually ineffective in mixed and take the woman out of the rally. Remember you lift, you lose.