Whats the best converter boxes for fringe reception area

For fringe OTA DTV, the antenna is the key component. The weak signal abilities of CECBs vary somewhat, but for consistently solid reception, you've got to have the appropriate antenna(s).

If your HDTVs have ATSC tuners, have you tried using those to get a handle on how challenging your OTA DTV reception will be? Could be a valuable data point for your location. "Older" built-in ATSC tuners have a more difficult time holding weak signals than the CECBs do. So, if they do an OK job on OTA, odds are your CECBs will do OK, too.

Do you have significant ghosting of UHF analog at your location? Even the more sensitive CECBs have been known to struggle with multipath interference. Analog ghosting is a good indication of the presence of multipath.

I believe the consensus is that DTV's have 5th generation tuners, while CECB's (especially the newer ones) generally have 6th generation tuners. This means you may see better station stability and maybe even more stations then your DTV's.