if your choice is campbell river or bamfield, fishing is definitely better in bamfield.
bamfield is on the west coast of the island; campbell river is on the east (inside) coast.
there is more variety of fishing (bottom fish, halibut and salmon on the west) where on the east you will be limited to salmon fishing only. generally the fishing is also better on the west.
pros of bamfield : bamfield is more remote and thus prettier and better fishing; can be awesome fishing
cons: poor access (float plane, boat ferry via port alberni, or road access via 1.5 hour gravel logging road which can be dicey and must share with seriously big a** logging trucks

; limited accomodations; more sensitive to weather
campbell river is easier to get to by car and thus faster access and definitely more "civilized". salmon fishing can be pretty good.
if you haven't booked a place to stay in bamfield for those dates, it may be way too late. most places are booked for prime time (end of june to labour day) one year in advance.
you may try my friends at Crown charters for charter and accomodations in bamfield. they run a nice operation and the accomodations are nice and new.
my 0.02