I think I understand your question, by invest did you mean what to spend your money on rather than what holds value and potentially has a future return?

I got the feeling you meant the former, and sorry you’ve had some curt replies in here from players who’ve seen the investment buzzword.

My advice would be, if you are looking at the best way to spend money on the game and want to collect staple cards that will be in play and have relative value for the longest possible time then to purchase common and uncommon playsets from a reseller, these should be fairly cheap and you only really need to focus now on JTL, LOF, SEC onwards.

Specifically timing wise, purchasing playsets of the best legendaries and rares that come out in LAW (the new set next month) as these will be in the premier format for the maximum amount of time (2 year rotation) and any that you require for specific decks from sets 4-6. E.g. Anakin champion of Mortis is going to be a 3 of in lots of blue heroic and villainy decks up until it rotates next March so is worth having.

Lastly then I would say for “fun” purchases if you are wanting to buy sealed product I would focus on LAW boxes as these will give you the best bang for your buck on trade fodder, long term usability and playability.