Define "better". Generally speaking there are more options for adding her as an AU and fewer for joint. If you apply joint it's not just your credit that will matter. If she's an AU then her credit won't factor into the approval decision.
zombieswontgetme wrote:Will it negatively impact my score
Depends on the usual factors. If you BT enough that the utilization is high it can. If it significantly drops your AAoA it can.