That's a tough choice. The 7698 has a little more gain for the 2Edge signals, better F/B ratio to reject interference from the NW, but a longer boom. The 2020 is smaller and has less VHF gain for KCTS PBS.
I'm more concerned about performance than price. Either one should be OK, but I can't give you a guarantee; the choice is yours.
2020
Bandwith 174 to 216 and 470 to 700 MHz
VHF Gain 7.5dB
UHF Gain 10dB
Front to Back Ratio 14dB
Boom Length 90.5"
http://www.channelmaster.com/Digital..._p/cm-2020.htm
7698
http://www.winegard.com/kbase/uploads/HD7698P.pdf
Boom length 168 inches
Same 7778 preamp.