To quote Deion Sanders, "Both!"
If you can get a difference maker then trading away draft picks is fine. Of course, with the CAP it can get more complicated because a guy in the prime of his career playing at an all-pro level is probably making a lot of money so the trade can have ramifications elsewhere on the roster.
I think the answer is make trades when it makes sense, and keep your draft picks when it doesn't. I am always willing to trade away picks 5 thru 7 for a player I need. Picks 1 thru 4 have to be good players.
Trading is also different for teams that are successful vs teams that are not. Losing teams are more than a player of 2 away so trading away draft picks that will be at the top of each round makes less sense. Winning teams are trading away picks at the bottom of the round and they have less value to them.
I really think a winning team has to be a player in free agency, trades and the draft. Drafting alone takes too much time and it means hitting on every draft pick. No one can do that. Even if you hit on your first 4 picks, in 4 years 3 of those 4 are going to be free agents. Keeping them while drafting another 4 starters every year is impossible. Getting a player you know is a star is better than a 1st round pick that carries a risk.