Blockchain.info, simply because i know them from when i started with bitcoin. Had my first bitcoin wallet with them and from then
I kept using them. For me there is on solid alternative.
My first blockchain site too. Never felt the need to change it. I remember that i once used a different one but the setup and interface of blockchain
is so addicting that i kept using them.
I say the same. Never had any transaction problem with blockchain.info wallet. Good site, stable, very informative and safe. The transactions fees aren't so high too. I recommend this service for who is looking for a good BTC wallet.