Your first pair of socks look great so a big congrats on completing them. For my vote for your next class, I'd go with the Toe Up Socks class to experience a whole different anatomy of knitting a pair of socks. The cast on is unique and can be used for other projects and you learn many 'new' techniques and ways to think about socks for you future knitting. I see that Essential Techniques is ahead in the voting but I think you would get that and more from Toe Up Socks since the price is 'up there' on both.
Just my $.02 as a sock knitter myself. Good luck with whatever you choose but again, your very first pair of socks turned out looking great and comfy!