Does size really matter ( This is about Tires)

[scuba dude]

I am going to replace my Mission tires and gotta question. I have a 2007 Big Sky 340RLQ same floor plan as 3400. I see that alot have gone with the G rated load range tires but I am wonderning about people that have replaced with same size E rated tires and had good or bad luck keeping them together on this size trailer that I have. What I have read here tells Bridgestone and Goodyear and Goodrich seem to be good tires but what size are we talking about.
Thanks in advance