For public proxies, it really also depends what you are using them for.
If you are going to use them in SB for scraping urls together with search operators such as intitle: etc in Google, prepare to have your public proxies get banned super fast.
Also, public proxies generally don't last very long at all when it comes to using them for Google scraping.
If you don't like using SB, ever thought of using something like proxy goblin? That thing scrapes and verifies public proxies 24/7. You will always have a fresh list to use without all the waiting. Wasn't to expensive too when it came out, like $25.