I'm in the process of ripping the carpet out of my mobile home and
replacing it with vinyl flooring. I've managed to cut the vinyl to the
correct size for one room. Now the hard part. The trim. What type of
trim is easiest to install? Is wood quarter round the easiest? What
about doorways? Also I want trim that will be wide enough to give me
some margin for error when cutting the vinyl. I need lots of margin for
error...

Rubbery cove molding ? Same margin for error as quarter round.