My antenna is behind the instrument cluster and I get 6-8 on the road. I even get 2-3 parked in my garage.
However, if I had a sharkfin or submarine installed OEM, then I would be using it instead even if it wasn't really better. That's just me, and I don't mind pulling apart trim in the car to run wires. The under-dash antenna is certainly less work in any case.