Just got an Iphone last weekend with Telstra after the missus has hers with Optus. Side by side, on the train smack in the middle of northern Sydney, mine shows full coverage. Hers has diddly. She's got the better plan but that means stuff all if you can't use your plan. Previously I was with Optus and cancelled the plan because I couldn't get coverage in suburban Newcastle.
After spending a bit of time in rural NSW, as well as bugerising around with the ADF, I'd never go back to Optus if you need coverage anywhere outside their Corporate HQ. It's nowt but shyte.