Can't think about any others altcoins while Ethereum is available to select as my favorite altcoin. Don't know much about Monero, doge is flying by elon which could be downfall anytime. Bnb is exchange coin only, still not used for any real purpose outside exchange. Won't like Bitcoin cash , rather original Bitcoin is better to hold which has blasted by record price already. But as op is asked for favorite altcoin, ether is my final choice as i have been using it since 6/7 years even more time and i can trust this coin more than rest of those altcoins in crypto market, even ether is flying Right now
Aside from ETH you should not have any favorite altcoins. Whichever altcoin generates money and i can gain profit by investing in it, i like that altcoin for that time being. When you love a altcoin and become really passionate about it then you won't sell that token even when it is necessary to book profit. In the short term it can help you ride a mega rally if it has any but in the long run it can ruin your portfolio because i saw many top projects become ashes in a few years.