Reply to Selling Serato SL3 for Traktor Kontrol S2 or S4?

Hey DJTT! I love this website, and the community . I just registered, and I just had a really quick question!

Right now, I own Serato SL3, two turntables, and a mixer.

However, I really want to switch to Traktor, and either pick up the S4 or the S2.

I'm in a bit of a predicament. I really don't have the money right now to go out and buy either the S2 or the S4. So I'm believeing of just selling my SL3, because if I just switch to Traktor, and pick up the traktor Scratch pro 2 for the 150$.

My question is which should I buy, the S2 or the S4?

Meaning, what are the major differences between the two?

Thanks again!