Generally I just default to blockchain.info. But recently it was acting funny and not showing recent blocks, and the search was broken. I stumbled onto blockr.io, and have come to like it.
Blockexplorer.com was experiencing strange database/search issues at the same time as Blockchain.info a couple days ago. Not sure what that was about. Ditto on blockr.io, though I'm not talking API.
If everyone was glitching, then it probably has to do something with the actual blockchain.