Kind of depends where you live and if you like all of the extra digital channels that are at 5.02, 5.03, etc. PBS HD only comes in with an antenna.
I think the biggest benefit of the OTA antenna is that you get a 3rd tuner because of OTA. So you can record 3 HD sources at once. It's already come in handy now that CFB season is here and has games on OTA HD channels. For example, last weekend my wife's tuner for Giada's Getaway on the Food Network didn't interrupt me from watching two games simultaneously (one dish tuner, one ota tuner) while the other dish tuner recorded her show for later viewing when I wasn't in charge of the remote.
I'd say definitely invest the $25 bucks in an antenna. Dell has the Terk iHDTV one for that price. Depends how far you are from the transmission towers to see if this fits for you. I'm about 20 miles and it works great. The payback was made for me in one game I didn't get to miss and now the rest is just gravy.