fiberglass is the way to go, but in 4" emt, steel is the The WAY to Go. keep the steel anyway. use gloves for fiber, you get that yellow splinter in your hand, good luck finding the thing ;0. if you are going to get sticks, get glow in the dark GR don't get china made stuff, invest the money in a good sticks.
they all have their place:
first time i saw a nylon fish tape i bought it and brought to my wire pulling crew in a condo we were constructing. they looked at it and on the first pull, they were really impressed with it and the guy pulling was commenting and at the same time went to cut the pulled wire from the fish tape and--yep--cut the eye off the tape!!!!
another tape that has it's place is the continuous fiberglass fishtape made by greenlee. we were called to a job that had a 4 inch pvc communication raceway that had been abandon and cut off at the floor. a sizable tenant had leased the top two floors of this office building, with the agreement that the building owner provide them a 4 inch raceway for fiber service to the building. the building owner told us this raceway was lost due to settlement of the building. and hired us to replace it. this required major underground digging up pavement and planters and the building's entrance fountain. it was worth a try to see if we could somehow use the original 4 inch. we used steel fish tapes to determine where the problem was which might allow us to dig only a small area for repair?? originally the raceway was full of water which we vacuumed out. as we fished the steel fish tapes to get measurements we could hear the tape from the opposite(not fished) end of the pipe??? we began to consider the pipe must be open for the sound to travel? i ordered(flown in) the continuous fiberglass tape (400 footer) from my supplier. this is the tape that is about 1/4 inch in diameter and has the footage on it. this tape allowed us plenty of puching power, where the stell tape flexed with spring tension. we started working the fiberglass tape and began to push through the obstruction. end result--one case--24 empty bud beer cans were dumped into the raceway. between the new tape and the vacuum system we cleared the pipe--called the building owner and told him we were finished! never told him that it was beer cans! might give our trade a bad reputation!
Metal fishtapes work well when your trying to locate where a plastic pipe runs under concrete without without wires or with wires (could be plastic plumbing drain pipe) Insert tape and attach cable locater to fish tape and follow signal. We've helped plumbers locate where piping is run in basements when they want to install a new bathroom in a finished house so they can make a correct saw cut.