Best is a matter of opinion. I've tried a few. My choice is MyFlighBook.com for a number of reasons not the least of which are (1) a very responsive developer, (2) iOS and Android apps in addition to the web interface, and (3) a downloadable, updatable Excel logbook so you can have a copy of the information locally. There's a pay-for option that will send an updated csv data file to your DropBox daily. Since I told this guy for months he should have a paid option, I paid my fee immediately!
I moved from Flightlogg.in to MyFlightBook about 2 years ago and have been very pleased with it.