Togepi

I am not up to date with all of the mons in future generation, but I think I remember someone saying that he has another evolution in GenIV.

This means you might want to evolve him all the way at some point.
With that said, it may be that the evolve candy cost is reduce to 25 from 50 when that happens.

My advice would be to keep it as it is, for later generations, and don't waste the candy yet...wait until it is cheaper to evolve.

A lot of this is speculation, but it will cost you nothing to wait.

Togetic needs less candies to be finally evolved into Togekiss in gen4, so Togetic is more valuable than Togepi.

Togepi can only be hatched from eggs while Togetic can be caught in the wild so I would say Togepi is more valuable. Although the spawn rates of Togetic is really rare.

I see this question a lot. "I have a 100% IV mon - will evolving it ruin it?" I dunno, evolve it and find out. a 100% useless mon is still a useless mon. A 100% evolved mon with a bad moveset is no less useless than it's unevolved (and relatively useless) mon.

All you're doing by not evolving it is putting off the inevitable (evolving it). It's like not opening a christmas present in case it's something you don't want.

Roll the dice, pray to the RNG gods, and evolve it for cryin' out loud.