Chemistry-bond energy
Heavier isotopes make stronger bonds, therefore C-D and C-T bonds are stronger than C-H bonds. The difference between the bond strengths is however not very significant and can be ignored for most practical purposes. 

Therefore, the extent of hyperconjugation can be given as: C-H > C-D > C-T (the difference however is not very significant).

The exact reason for this little difference involves a quantum mechanical explanation, which you should not bother about if you are studying high school chemsitry. If you want to read that, you can refer the links in the comment section.