You should have defined if the short position would be scaled/risk adjusted for beta/volatility. SPY is obviously less volatile which is nice when you're losing money in a short. Much of the real crap is contained in IWM so I would rather short that.
All of them (Dow, SP, Nas, Russ), and then manage them according to how they go. Essentially 4 positions and you can take profits as it happens to manage risk. If the trade is good, it will be good on all. Usually there is rotation, etc. so the timing (measured in hours- maybe days) will be slightly different. Use that to your advantage to manage the risk.
SPY cuz shit's slow to rebound and full of boomers stocks. Ain't nobody got time for that. We all driving new Teslas buying new iPads on Amazon and wearing Etsy hemp sweaters
QQQ QQQ is up 46% compared to 15% for SPY in 1 year. IMO ....... QQQ would drop further than SPY in a bear market.
i don't trade any indices intra-day, just long-term, but no matter what happens I will never short the US indices.