Determining whether YAC or BAC vectors are better depends on the specific research goals and requirements. Each vector has its advantages and disadvantages. YAC vectors have a higher cloning capacity and can accommodate larger gene inserts, making them suitable for cloning large fragments of genomic DNA. However, they tend to be less stable and can experience chimerism and rearrangements. On the other hand, BAC vectors are more stable, have a lower cloning capacity, and are easier to manipulate in bacterial systems. BAC vectors are commonly used for large-scale genomic sequencing and functional genomics studies. Ultimately, the choice between YAC and BAC vectors depends on the specific experimental needs and the characteristics of the target DNA.