top in what sense?
there are so many different factors that you can compare cryptocurrencies.

- market cap? check www.coinmarketcap.com to see the list
- price? again check above site or any exchange for that matter.
- ability to make profit? all of the altcoins can potentially be that if they are not dead. they can get pumped.
- technology? opinions are different in this matter. i say only XMR and that is of course after bitcoin.