Can't beat a good old discone for wide band coverage. https://www.amazon.com/Tram-1410-Discone-Scanner-Antenna/dp/B00QVPGKHU
But do you really need the 180Mhz-390MHz range? It's usually mil air and conversations like "Turning right....Now!" and such exercise commands. Maybe you only need a dual band antenna, 150Mhz / 450MHz which would give you more options? The more narrow the frequency range the easier it is to get the proper antenna.
it will be outside w LMR400 cableThree questions for you that will get you better qualified responses here:
1) Is this for indoor or outdoor mounting?
2) Are you looking to build (DIY) or buy?
3) How much are you wanting to spend?
Consider using a remote switch at the antennas. The cheapest one are probably a $10 Vertical/Horizontal polarization switch for sat dishes LNB heads. They switch at 15volt DC that you feed the coax from a bias-T down at the scanner.I would have to bring a separate cable down with a type of junction box with an A & B switch
"Best" depends on your budget. You can get discone antennas from $50 to $4000.I don’t listen to anything below 119mhz. What’s the best discone does anyone suggest?