Let's notice that both the SPDR S&P 500 (SPY) and the iShares Russell 2000 Index (IWM) peaked last week within one day of each other.
However, the SPY high occurred after a sharply-angled advance, while the IWM advance ended after a sideways rally that failed to sustain a thrust to a new all-time high.
In addition to showing relative weakness into last week's high, notice that the ensuing bout of weakness represented a 3.3% decline in the IWM, but only a 1.3% decline in the SPY.
Finally, my trending MA's in the SPY rolled over into a sideways configuration, while the same MA’s in the IWM triggered a negative cross-over (near-term sell signal) late on Oct 29.
Right now, on a relative basis, one would much rather be long SPY than IWM, and/or neutral SPY vs. short IWM.