Choosing between ACWI (generally any "all world", MSCI, FTSE, Solactive, ...) and pure SP500 is pretty tricky, they are two very different beasts. Not sure where you're based, but for SP500 you might want to consider a swap-based ETF (instead of replicated). Swap-based might be a bit more tricky ("what if the counterparty fails", that's why it's a good idea to see who is the swap counterparty, is it "too big to fail", is there only one or multiple etc) - but it will give you a tiny boost to profits, as swap-based ETFs do not pay 15% WHT on SP500 dividends. That being said, SPYL is a good, safe choice, might not be worth overthinking it. As for the "all world" ETFs it's tricky to compare them as they very often use different index providers (ACWI, ACWI IMI, FTSE, Solactive, ...) and therefore hold different stock. You can either use factsheets to compare what they hold, or you can use something like AZbyte to compare their contents - but you'll quickly notice that they are ~90% similar (VWCE vs ACWI are 96% the same money-weighted, ACWI being cheaper so probably a better choice long-term; WEBN is not yet in their database). Therefore if I might suggest, compare their TERs (VWCE is by far the most expensive now so shouldn't be recommended), then their TDs (if you can = if they follow the same index), and general history of the issuer (iShares, Vanguard and SPDR being the most well established and not having a history of fucking you over, and Luxor/Amundi having history of closing ETFs if they don't grow quickly enough = yellow flag, you won't lose your money but you might have to wait weeks for them to return your cash if they decide to close WEBN; I doubt they will but hey, they closed few before). Also, once every while check if a given provider didn't open a cheaper version of a current offering (I'm talking to you, iShares). More on reddit.com

The number of shares in an ETF or mutual fund are of no relevance to your position. All that matters is the initial and future number of dollars you invest. Two S&P investments, all things being equal, will rise and fall together. I would buy the one with the lowest management fee. For example, my favorite, especially in an tax deferred account at Fidelity is FXAIX. the fee is only .015%, which I think is the lowest around. More on reddit.com

Yes. More on reddit.com

I asked this myself on this sub like 6 months ago. The answer is SPY is more liquid with more volume so its better for options and day trading. VOO is the preferred fund for long term investors where expense ratios matter. It also makes sense about liquidity because most people buying SPY are trading while most people buying VOO are holding. More on reddit.com