Futures are preferable. ETFs could be useful during a volatility spike if you have a small account. Lets say the ES starts having a 100 handle daily range for a while. You might want to trade 100 lots of SPY instead of one lot of ES in that kind of scenario.
I prefer the NQ and ES. And I say $10,000 to trade 1 contract, risking max $200 per trade. Trading USA regular market hours. Good trading to you.
I think your question is Index ETF or futures better? My choice is Index futures. why ? - volume much higher - higher leverage. I don't have to put in so much money in my trading account. also I can trade greater quantity, hence greater profit ( or greater loss for some people ) - in general, greater trading hours
See here: https://en.wikipedia.org/wiki/Spread_betting#Financial_spread_betting For whatever reasons, it isn't authorised in many countries. Despite the name, it is hardly different from trading using other means of market exposure, though at least in the UK, spreadbetting profits have zero tax implications.