For reference, you’re comparing a Target Date Fund (TDF) to a world index fund. A TDF is composed of stocks and bonds and slowly shifts towards bonds as it reaches its target date (the date is ideally “your retirement date” - the one you’re looking at is for 2020). The world index fund (VT) is an index of every stock in the world, so by buying one share you buy a piece of everything that exists.

Unless you’re retiring very soon, you should generally just buy VT and forget about it. If you’re close to retiring you might want to think about a “bond tent”, where you increase your bond percentage incrementally up until you retire, then slowly sell your bonds after you retire. You can do this by buying a bond index by itself.

There’s a few “right” answers to this depending on what you believe so I would do more research and understand what all of this actually is. The good news is that proper investing is actually really easy. The best strategy is generally to “buy the entire haystack, don’t ever sell”. The Bogleheads wiki is a good place to check first to get some of the basics down.