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 you are a mean reversion trader and wanted to try trading an index then why would you pick QQQ instead IWM? That makes no sense to me.
I am not sure what you are using but just a casual glance at the price charts should be enough to tell you which one to trade. It doesn't even need any complex tools.
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.