Another excellent question. The real (incredibly stupid) answer? I originally told my prop firm I don't need Amex quotes. QQQ and TQQQ are NSD, so I went with them. BTW, I tried TQQQ just to manage risk better because of the liquidity. What a stupid idea for an extremely short term trader. (Bring on the TQQQ hate) If there were any ETF I were to trade, it would be IWM, but I still don't think it would have mattered. I think it would still have been a necessary subconscious kick in the ass.
But to be clear AGAIN, I do not trade mean reversion in any index. Just stocks. That would be fucking suicide. An 8 year old with an IQ above 75 could should know that.