'best' is there a single item ....the above replies correctly show there isn't.
So, a different view (excluding directional, noisy bird perches etc. which have little place in the mobile scenario).
The top one is the one
I use most often for airband - Nagoya NA-771 dual-band amateur. Other makers do the same basic thing with similar numbering. First one like this I ever bought was from Revex. Flexible and works well for milair despite not being designed for it. Length is ok as it's very flexible. Longer flexible would be unwieldy.
Next is a (Waters & Stanton) Watson W-901 'air gainer' - expensive rubbish but better than the piece of bearcrap at the bottom
No3 - Watson W-801 'regular gainer' - see above but aimed at scanner enthusiasts instead of airband. Electrically identical to the 901
No 4 - a Watson that is a bit more useful. Telescopic so can be 'tuned' to some extent in use. Has a flexible joint so can be angled and helps with safety. When fully retracted its a touch smaller than the bearcrap, fully extended in the photo.
No5 - another favourite, Maldol AH-W1000RX. Two flexible joints which mean it can actually be folded downwards (surprisingly useful in crowds where you'd normally need to use a relaively short flexible whip), max length 1000mm so very 'tuneable'
No6 - Yupiteru standard telescopic. They downgraded to a short whip on later models. Cheap as chips, tuneable. Again has the flexible joint
No7 - Don't remember what make. 550mm telescopic with pocket clip. Handy as a backup but without the flexible joint it could place strain on the BNC/SMA plug if bumped.
No8 - some piece of crap that came attached to a bearcrap. Only advantage is it looks more like part of the receiver? For reception a damp cabbage leaf would be just as good.
Not shown - 'broadsword piece of wire. Darren siezed a piece of market - Watson are over-priced. Take a piece of copper wire, solder it to a connector and then shrink wrap it. Cheap and will do the job. Downsides, look battered when new and get worse, might as well make one yourself and save the money. Certainly not worth paying the postage on.
I have others but they never see the light of day and are variations on the theme rather than offering anything to the discussion anyway.
So options and ideas rather than 'best'....................