To determine which group is the most advanced, we need to define what is meant by "advanced."
In general, we could say that a group is more advanced if it has more complex structures and functions, is better adapted to its environment, and has a greater diversity of species.
Based on these criteria, we can eliminate Bryophytes and Thallophytes from consideration as the most advanced group. While both groups have important ecological roles, they are generally less complex and less diverse than the other two groups.
Between Pteridophytes and Gymnosperms, it is generally accepted that Gymnosperms are more advanced. This is because Gymnosperms have evolved some key adaptations that have allowed them to be successful in diverse environments. For example, they have evolved a woody stem that allows them to grow tall and compete for sunlight, and they have developed seeds that are protected by cones, which allow them to disperse to new areas and survive harsh conditions. Additionally, Gymnosperms are generally more diverse than Pteridophytes, with over 1,000 species compared to around 12,000 species of ferns and other Pteridophytes.
In summary, Gymnosperms are generally considered to be the most advanced group out of the four options listed, due to their complex structures, adaptations, and diversity of species.