Tom is better than I at maths 还是 Tom is better than me at maths

1. 都可以.
2. 按照语法来说,than是连词,后面引导比较状语从句,且从句经常只保留主语（有时也可加谓语）.
所以,最好是：Tom is better than I (am) at maths.

3. 但是在日常使用尤其是口语中,也把than视为介词,所以Tom is better than me at maths.也是可以的.