A key factor in Aldi's climb to the top was its value for money - despite some customers complaining stores were "untidy" and looked like "a jumble sale".
In the online category, shoppers were asked about the convenience of delivery slots, the choice of substitute items and drivers' service, as well as quality, product ranges and overall value for money.
The second favourite supermarket was Marks & Spencer (LON: MKS), followed closely by Lidl and then Waitrose (LON: JLH) falling into fourth place.
Customers prefer Aldi's special offers and high quality fresh and own-label produce.
"With food costs rising it seems as though shoppers have felt the pinch and are voting with their feet and wallets", said Alex Neill, managing director of Which? for home products and services.
What's more, the latest quarterly sales figures show that Aldi and Lidl's sales rose by 16.2% and 16.3% respectively compared to Tesco's 2.6%, so it's not hard to see why Tesco might be eyeing a bold new strategy to tackle the threat head-on.
Lidl was voted the worst of all supermarkets for queuing times, Aldi and Iceland's staff availability disappointed and Waitrose's value for money scored the worst.
The German discounters pose a genuine threat to Britain's established "big four": Aldi and Lidl now account for £1 out of every £8 spent at United Kingdom supermarkets, according to research from Kantar Worldpanel.
"The big four supermarkets need to up their game or risk losing their customers to other supermarkets who are doing a better job of giving people what they want", she said.
Since then more than 700 of its shops have sprung up across the United Kingdom and Ireland, luring consumers who value the group's cut-price product offering; and its stripped-back, no-nonsense approach to groceries.
Iceland received five stars for its drivers' service and the availability of delivery slots, with 76 per cent of shoppers saying their most recent order was delivered on time.
Among the online supermarkets, Iceland claimed the top spot for the third year running, but shared the title with Ocado for the first time.
The big four supermarkets - Tesco, Asda, Morrisons and Sainsbury's - languish at the bottom of the in-store survey.
Amazon Fresh, which launched in 2016, has been included in the online survey for the first time, coming in fifth position.