That is always a relative question to the state of the technology at any given time. So it is always changing and in a state of flux. My favourite has been Chrome – which with the Bing Tab and iChrome tab works for me. But I have been impressed with Windows 10 The Edge which is intuitive and useful for students to do their research with as it has direct links to OneNote which means whatever you study can be captured and stored. Not only that The Edge would be useful for teachers as it really works like an interactive board software – with its link to OneNote and the potential with Office 365 ClassNotes webapp will be all the tools teachers at secondary level might need. All run from a tablet or laptop.
But I have recently re-looked at Mozilla’s Firebird and found that this browser is fast and clean . Perhaps doesn’t have the bells and whistles associated with other browsers but if you want a basic browser that is one of the fastest to use Firebird’s present version is good