The question is which format you're interested in playing. If you're wanting to play standard, then you're likely going to have to just resign yourself to trading to get the newer cards. If you're wanting to use your older stuff, well, then you go with Modern or Legacy, at which point you'll likely have to pony up some cash to fill out your lists with the more expensive older chase cards... it's a bit of a catch-22 for the casual player making the move into more competitive play...
Personally, I would suggest getting into standard, as it's an ever-changing format with rotation and the like. But that's just me. If you go with the more eternal formats you're likely going to run into many of the same decks over and over, with just tiny changes here and there.