As already mentioned, the HD HomeRun makes a great test meter. Using the HDHomeRun Config Utility that was supplied with the box, you can tune to any real channel with out scanning. You then have real time readout of raw strength as well as signal quality... great for fine tuning antenna location and aim.
http://forum.tvfool.com/showthread.php?t=820
I agree with the HD7000R recommendation offered by teleview, though I would not have any concern if you opted for a larger antenna, particularly if you are intent on making an attic install work well. Larger 7000 series antennas from Winegard are good choices, though they can be very challenging to re-fold if you need to remove them from the attic. Antennacraft C290 & C490 are much easier to refold as are the Channel Master CM3016 & CM-3018.
Besides reduction in signal level and quality, attic mounting puts your antenna closer to devices in your home that generate interference (computers, florescent and LED bulbs, motors, etc.) so outdoor mounting is almost always a superior choice.