Hi There,
As above - it depends on what pleases the individual. For myself, it depends which set it might be. For example with Select sets, I am trying to complete as close to a master set as I can of each of them, with exceptions, where I can't justify the cost of buying. I have a few Champions release Master Sets but I am willing to accept that there are others I will never achieve a Master set for, either due to cost or availability, so will complete as much of the remainder as I can. Which in itself can involve a pretty penny at times. However, since ESP/TLA have started, with the explosion of parallels, I have become a Team collector and aim to collect every Parramatta card that comes out each release (except for the Power Play cards which I didn't get into). In addition to which I pick up a full base set for each release. That's something I can justify and generally achieve given time. Also, I don't buy a lot in terms of boxes or packets, I generally pick up what I want on the second hand market, so I get exactly what I am looking for.
The odd decent hit I have made from buying packs and boxes, I have in the initial instance, offered on here for trade for something of equivalent value that I am after. Sometimes a trade or sale has ensued, but if not, the card goes back into storage, until I eventually get my cards more sorted and an extras list together, then might throw that up here.
After all that - it comes back to the beginning - what pleases the collector, in this case - you. Have a think of how you would like your collection to develop and look down the track. and work on a strategy to complete that goal. Once you have decided what/who you want to collect, you can make a list of your needs and go searching the second hand market for those you want/need to complete you goals. Starting on here would be a great jumping off point, as the collectors here are all sensational, and are in it as collectors, not to make a buck, and always willing to help if they can.