Best for what purpose?
If beautiful colors are your thing, then panthers are never dissapointing. They are more expensive though.
Jacksons have those awesome prehistoric looking horns and are easy to come by.
Veileds are known to be the most hardy and adaptive and are therefore suggested to beginners as a first chameleon. They are also the least expensive to purchase
If size is your thing, mellers and parsons get HUGE. (veileds can get quite big too though)