Oh boy, this logic is unfortunately quite a bit off. Please do not invest until you have understood what it is that you are buying.
So, to give you a starting point. What you want to buy are shares of companies, like Apple, Microsoft etc. Then you need to decide at what proportion you want to hold these shares. The allocation by market capitalisation is very practical, because it is a self-rebalancing one (you don’t need to constantly tweak it).
So you would like to ideally hold thousands of shares and own each company proportionally to their market cap, but doing that manually would be a nightmare. For this we have indexes, like S&P 500. But you cannot just buy an index. An index is just like a recipe. What you need is an index-based Exchange Traded Fund. What they do, is that they try to replicate the index for you.
Now, coming back to your question. Check exactly what kind of indexes these ETFs are based on and what are the biggest companies. You will find that one is based on a FTSE index, the other one on MSCI. But both of them will have the same top 10 companies. Both will be almost identical, with small differences between the indexes.
Well, I wrote more than I planned to, but I still only scratched the surface. I think it’s important that you at least understand the basics before you invest.
I suggested this once and we do have a wiki section, but nobody is contributing to it. It would take quite some effort to organize our knowledge, many people would have to contribute. You can make some suggestions on how to restructure our wiki, maybe this will motivate people.