I can answer your question with the following information. From SEA, UA switched its 744 flights to NRT to 777s, and AA switched from MD-11 to the 777 on this route, as well. Asiana is switching to the 777 to SEL, replacing 744s. Now, KE operates 777s to SFO and LAX, replacing 744s. Although the 744 dominates the trans-Pacific market, the 777 has certainly found a niche on some of these routes. As far as which is safer, a large twin has yet to have problems with engine reliability. Keep in mind that with a four-engine aircraft, there is twice as much to go wrong than on a twin. I would feel equally safe on either, but I cannot say the same for everyone. I hope that helps. Welcome to the forum!