I remember the days when an input had to have "medium priority" to be able to add other inputs up to 1 kB in a zero-fee transaction. It's too bad the concept of "coin days destroyed" was bandoned in favour of higher fees. It was a good feature, as it rewarded using older funds, while discouraging rapid (spam) transactions.
I gave up on it before it was abandoned, after some of my transactions got stuck for 2 weeks and I had to double spend them to get them confirmed.