I pay attention to the market, because I am interested in things like business and finance and geopolitics. I look at a lot of data, including several popular indices such as the DJIA and the S&P500. However, when I want a single quick look at "how the market is doing," I look at SPXEW, the S&P 500 Equal Weight Index. I use this because I feel it gives me a more honest opinion about how each of its 500 large component companies is doing. The S&P500, on the the other hand, tells me mostly about how the dozen or so biggest companies are doing. It's cap-weighting methodology skews the data.
I saw a question on this sub recently from a fella who felt like the S&P500 was overpriced from a p/e perspective. This caused that fella to not want to buy the S&P500 right now -- which is market timing, and therefore non-Boglehead.
However, you would get exactly the same diversification -- i.e., buying 500 stocks -- buying an ETF based on the SPXEW as you would buying an ETF based on the S&P500. The p/e would be different. Obviously, the proportions of the component stocks would be different because the indexes weight differently.
How do you Bogleheads feel about this? I am aware that the S&P500 often does much better than the SPXEW.