Its really hit n miss.
I live in a bit of a valley and ota hd came in very poor. I tried a few radioshack antennas. One day I'd get a hd channels fairly, the next day none.
Then voom (remember them ) came along. Their tuner also got ota hd and as part of their install they put on a ota hd antenna on the roof. It worked poorly like the ones I had tried on my own.
Then voom came back out and put a larger one on the roof, and still reception was choppy.
Finally voom came back out and put an extension onto the antenna and I then could get everything 100% perfectly.
Voom never charged for these antenna's and came out for free, until my ota hd was up and working.
It would have cost me $300+ to have a private company do all this, that voom did for free as part of their free install for the voom system.
Then... voom went belly-up, but never came out to get their equipment (except the receiver). So basically, I got my ota hd problems solved and a nice working antenna that I still use today, all for free thanks to voom.
I really liked voom. I still cant believe they never caught on. What a loss.
So, its hit and miss.