Firstly congratulations. Nice choice to have. Personally I’d go for 787. There are many more 2 crew trips on 777 which are lower credit and much harder work. As a junior you will be doing more of them . Just had a quick glance and of the most junior 30 on each fleet 7 fo’s are doing 5 trips in jan on the triple. 1 on the 787 for the bottom 30 .