is a Air / nav transceiver Ht best for Civil ?
For general purpose scanning, generally no. While most have tighter airband-only rf passbands, and loud audio, sensitivity is not better than say a 396xt. It is only designed for short-range contacts to say the FBO or tower while actually at or near the airport.
Scanning is typically a cumbersome process to program, and much slower than your Uniden, which has far more useful features.
One small improvement you can make is to use the commercial airband ducks that are used like the Icom FA-BO2AR (bnc) or Vertex-Standard ATV-10/q3000194 (sma). The semi-rigid ATV-10 fits nicely on the 396. However, this is only a minor improvement in weak-signal reception, and being tuned to airband specifically, gets you away from other vhf-hi signal territory. In other words, is won't perform miracles, but is noticeable over the standard Uniden oem duck and may provide some protection from vhf-hi overload by being specifically tuned.