Which looks more expensive today: the S&P 500 or Nasdaq?
On the current data, U.S. Large Cap has a P/E of 27.00, while Nasdaq 100 Proxy has a P/E of 31.58. On P/E alone, U.S. Large Cap looks cheaper and Nasdaq 100 Proxy looks more expensive.
That comparison is only a starting point. Different markets can have different sector weights, growth expectations, interest-rate sensitivity, currency risk, accounting rules, and ETF methodology.