A few threads that may be helpful:
http://forum.tvfool.com/showthread.php?t=13236&page=5 (starting with post #87)
http://forum.tvfool.com/showthread.php?t=13530
http://forum.tvfool.com/showthread.php?t=13583
http://forum.tvfool.com/showthread.php?t=13646
A low noise figure is always desirable. High gain is not always helpful. Total up the losses on the output side of the amp to determine how much
may be needed. But also consider how much signal power you have from the air + antenna gain - down-lead to preamp. Too much signal power can cause just as much trouble as too little.
FWIW, For some time now, the RCA TVPRAMP1R has been my choice for most applications. Low cost, low noise, plenty of gain, dual inputs and an FM trap that can be switched in or out.
I'm looking forward to testing the new Antennas Direct preamp. I've got a sample in hand but am recovering from shoulder surgery so have to stay off ladders and roofs for a bit longer.