Most of my blocks that have been staking are 50 from mining. I bought a bunch more, and broke them down to 100, 500, and 1000, depending upon how lazy I was at the time. My wallet has been open the whole time, and staking like a beast. I've got blocks of 50 that have 9000 confirmations, so they can take a long time to stake. My oldest block of 100 has 4900 confirmations. My oldest block of 500 has 3200 confirmations, and my larger blocks have already staked and split. I haven't really paid much attention to it, until now.
It looks like blocks larger than 1000 will stake the quickest, at the cost of less blocks to stake. I'll try to pay more attention, and post my findings.