I would say (like a lot of people on this thread) it depends what you're playing and with who.
If you're familiar with those around your table, aggressiveness (WHEN POSSIBLE) is the way to go; knowing your opponents game and their style is perfect when playing aggressive because you know when and how much to raise enough to get a call. That doesn't mean you won't be occasionally passive and slow-play/trap when possible. You should, imo, never play just aggressive or just passive. You should prioritize one style, but be rounded well enough to play the latter when needed.
As for passiveness, I usually like playing tighter when I don't know who I'm playing against because it not only minimizes my losses, but it gives me several hands-worth of information on my other opponents that allow me to have a minimal (but much better) understanding of their style of play. Especially in online MTTs when I'm nearing the bubble, and have just been moved to a random table w/ randos, I play much more passive until I have a solid read/understanding of who's passive and who's aggro; then I play aggro v. passive players, and passive vs. aggros/wild cards.
If you're playing
freerolls, it's a free-for-all in the first levels (no pun-intended) and I usually shove with top 7 hands and call shoves w/ mid-high pairs if I notice the shover is tilted.