I personally think the best view is just a little bit down from the main road above the town.
As the most scenic view would be at sunset with the Dome of the duomo in the scene and looking out over the town's colorful houses built into the cliff as well as sea all at once.
The main road (Amalfi coast drive is SS 163) ; to get into Positano main town you would take Cristoforo Colombo.
Shortly down this road, just a little higher up than the Marincanto Hotel sits.
There are areas where you can get a good look (not private property) from roadside or even the hotel parking area there.
This is the type of view I am referring to:
https://500px.com/photo/74584329/sunset-time-in-positano-by-mihai-cazacincu?ctx_page=1&from=search&ctx_q=positano&ctx_type=photos&ctx_sort=pulse
If Bruno Restaurant mentioned above is the small place with outdoor tables on the water's edge side, then that is very close to where I am talking about.