What are some good wifi cards for "wardriving" nowadays? Something USB, with atleast AC standard (2.4 and 5ghz support), and with a good linux support (monitor mode, etc.)?
No messing with GPSD, no tuning, absolutely nothing just supply power and you are ready to rock.
Additional benefit: you also detect cell towers & bluetooth if you wish to do so.
For extra good results, drive... slow... I use a scooter that allows me to comfortably drive 20km/h (15 in Freedoms) with a plastic case on the back with a handful of phones and can easily get about 80 / 90% of the SSIDs.
I VERY seldomly wiggle, am in the 600 - 700 range.