I do like the "X" cross for its added exposure and helplessness of the victim. She's unable to even close her legs together to try to protect herself.
Her very last shred of modesty is taken away, and her most private parts are on display for everyone to clearly see as she struggles.
And the crowd is right there watching her suffer, completely exposed.
The problems with the "X" cross are that one like the one shown here requires some skill to cut the three-way joint where the three timbers join. And with the legs spread, a victim would tire more quickly and perhaps die sooner than one on a "T" cross.
The "T" cross was easier to make and probably more commonly used. If the upright stipes was a squared-off timber, then the victim's legs would tend to sag with the knees together when she was hanging, so not as exposed. But if the upright post was round, then with her feet nailed side by side, her knees would tend to project outward to each side, leaving her more exposed.
And the view from behind is not blocked by the arms of the "X" cross.
The downside was that she could, if she made the effort, close her legs together, particularly when she was struggling to raise herself.
But she would be mostly completely exposed then, too.
There would have been no way for her to protect herself from further tortures.
And with her legs positioned so that she could push herself upward more naturally than with them spread as they would be on the "X" cross, her suffering would have gone on perhaps for several days before she grew too weak to raise herself. So there are reasons why one might choose either of these two crosses; with the "X" cross there was more exposure and perhaps humiliation, but with the "T" cross the display might last longer.