It's much easier to identify the best cordless phones today than in the past. For a start the contenders are all DECT 6.0 phones. As a consequence they have few if any problems with WiFi interference, call quality or range. In other words the are generally more than adequate for use around the home, however that's not say there aren't differences between them and some are a lot better than others.
The AT&T SB67118 is a DECT 6.0 phone. It's definitely the best cordless phone to use in situations where cordless phone range could be an issue. Optional signal boosters can be added. They dramatically increase coverage and can also overcome issues with blind spots.
The quickest and best way to compare cordless phones is to first identify the type or category that is of most interest. Having reduced the field to a manageable number you can more easily compare apples with apples when deciding on the best cordless phone.