Which is better: preserving Fajr prayer in a specific mosque to achieve "he for whom forty men testify to faith shall enter Paradise," or moving between mosques for fear of being among those who "pray so that it may be said that so-and-so is a worshiper"?

The best mosque for performing prayers is the one whose Imam recites correctly, holds sound beliefs, and possesses righteous deeds and character. Next, it is the one with the largest congregation, because the greater the congregation, the more multiplied the reward. It is also commendable to choose the mosque that is further away, as Allah records the footsteps for walking to the mosque; every step elevates a rank and removes a sin. Furthermore, congregational prayer can exceed individual prayer by more than twenty degrees. One may also choose a mosque where righteous people gather, to benefit from their company in knowledge and character. This does not mean one cannot pray in other mosques occasionally, provided it does not lead to the neglect of the closest mosque. However, if the only way to avoid showing off (riya') is to pray in several mosques, then there is no harm in that.