The ATAS 120 is super convenient for use of multiple bands but because it operates on multiple bands it *has* to compromise its efficiency on many bands. The ATAS is mostly meant to be used on HF bands. In my experience it is very convenient when combined with a Yaesu radio which can command it to change its configuration as you move between bands, but it is by far not the best HF antenna for pure efficiency.
Food for thought: When I'm out and about wheeling I use almost exclusively 2 meters and a little bit of 440. This gives me plenty of range to use the local repeaters and to talk to other vehicles in the group. To this end, I have 2 2 meter / 440 antennas that I use:
My primary antenna is a Diamond 2/440 (I forget the model number) high gain antenna, it has somewhere around 7 db's of gain on 2 meters. The down side is that it is very rigid. Due to the rigidity, I remove it and replace it with a much more flexible, but lower gain (around 5 db's as i recall), antenna when I wheel where there is low hanging branches.
To this day I still use mag mounts to hold my antennas because they act as a very nice mechanical "fail safe" if I mis-judge how low a branch hangs for example in which case the mag mount will let go, the antenna will fall over and make a heck of a noise but nothing will be damaged or broken.
