Try the Zn (10 Year US Treasuries)
Forget the SandP, it pings around all over the place and you'll be stopped out of your position before you can say 'what the'.
US Treasuries are a slow market, they can take a while to move but if you want to learn how things work then it's the best. It tends to stop at the right points in terms of support and resistance, unlike the SandP which can overshoot a fair bit before coming back.
The Treasuries are a 'thick' market. As in the order book is thick, as such it takes time and effort for the orders to be eaten through before price can move. The SandP and other indices have thinner books, meaning price is more volatile as there are less positions/orders to be eaten through, meaning that price can move quite violently and at great speed with less exact support/resistance levels.
Have a friend at a prop firm who got me onto the ZN. He said he had never bothered with the SandP as he could never figure it out. This was a bloke who writes trading courses for them as well. So I decided to pay attention.
He also said the Bund and Eurostoxx were great markets but to be honest if you can't master one market then you're not going to master 2 or 3. I would advise sticking with the ZN, slow as it is, and to work on making your fortune on that first.