I use blockchain.info , same like most of people here, from what i read. I'm guessing it's hard for other competing sites to get users to switch their
habits and preferred block explorer when the one they're using is doing the job almost flawlessly.
Only in cases where there's some sort of downtime, or other unavailability i'm forced to use blockr.io as an alternative, but i don't find it as good,
so i bounce back to blockchain.info asap.
wouldnt call it near flawless at all, they have a problem with accepting spoofed transactions into their ledger, transactions that dont even show up on any other block explorer.
https://www.reddit.com/r/Bitcoin/comments/3fv42j/blockchaininfo_spoofed_transactions_problem_aug_4/just one of the links that can be found. after learning about these incidents ive since switched over to blockr.io