the title says most of the question...
What altcoin do you have of most value, or is your favorite...
This can mean you hold a lot of it, you use it for a lot of your transactions comparing to other coins, etc
You can choose multiple coins, just explain why you think it's the best coin in your possession

I would pick ETH. Many people said that it will go to its IPO price but I feels that ETH is currently forming the bottom before going up again.