Epiphany is usually the first choice for GNOME users who want to use a web browser which is lighter than Firefox and integrates well with GNOME. Of course, there are alternatives like Konqueror or Opera out there, but they are either too bloated compared to Epiphany, or they don't integrate very well with the GNOME desktop environment. Being the default web browser in GNOME and built using the GTK toolkit, Epiphany became over time a well-known web browser especially for the fact that it is lightweight and has a basic, clean interface.
Epiphany Browser 2.26.1 running in Ubuntu 9.04 Jaunty Jackalope
The rendering engine used by this browser is the same as Firefox, Gecko and has a score of 72/100 at the Acid3 Test. By comparison, Firefox 3.5 got 93/100, Opera 10 Beta got an impressive (and expected) 100/100 and Konqueror 4.2.95 (included in KDE 4.3 RC1) got 89/100.