I would actually evolve it either right away or at level 26. Another option is to never evolve it.
The only move that is worth teaching it is Thunderbolt. This can be taught to Raichu using the move relearner. Or even by TM if you want. However, if you don't want either of these, you can have Pikachu evolve after learning Thunderbolt.
The other option is to never evolve Pikachu. This is if you get the Light Ball item, which makes Pikachu arguably more useful for ingame (and some might contend competitive also).