Maybe there is a better alternative out there, but I am sticking with the Coinmarketcap as I got used to it and I am not really in need of any additional info, but I found a similar site where you can see the difference in current value and the ATH value of the coin (in %): athcoinindex(.com)
I also stayed on a Coinmarketcap. I've been using this site for a long time and I really like it and I've gotten used to it. It is very informative, has a small number of ads and is easy to use. Sometimes I use other popular sites, but it's rare.