Most overvalued coin?
0. Ripple, must be ~0.20$
1. Ripple
2. Ripple
3. Bitcoin Gold, must be under 50$
Most undervalued coin?
1. Dash
2. Monero/Zcash
+upvote for this, XRP lovers must take a close look on the charts, seems ~0.20$ is legit price lol

Ripple is a project which has its flaws, and also has its pros. I for one have held on to a little bit of ripple for months now, and it has given me very nice returns.
Going back to the OP, to decide which is the most undervalued coin, we should probably start looking at coinmarketcap's most valued, and decide if that value is legitimate. Bitcoin is clearly the culprit, it is definitely the most overvalued coin at this moment. It doesn't perform nearly as well as some other coins do, its earned some of that price being branded the digital gold, store of value etc etc, however the majority of that price is hyper inflated by the media. Turn on the news, grab a paper, or scroll through some news portals online - how often do you see the word bitcoin compared to last year? How many stories you can read of bitcoin millionaires?
People love the hype, and want to be part of it...