Outfox the Market 鈥 launched in 2017 to take on the big energy providers 鈥 has come top of an annual Which? user survey.
The Leicester-based business topped the survey due to its cheap tariffs and good customer service.
Some 25 energy companies were rated by 7,460 people in the customer satisfaction survey, with the independent provider moving up to first place from 19th last year.
Which? said customers were most positive about the accuracy of its bills and value-for-money.
However it said despite topping the table, it wasn鈥檛 making the business a Which? Recommended Provider because it didn鈥檛 respond fully to its 鈥減rocedures questions鈥 and had had to be ordered by Ofgem last spring to pay more than 拢600,000 for the feed-in tariff scheme.
Which? said this year two other energy companies had impressed it enough to earn its Recommended Provider award 鈥 Octopus Energy, which has a big call centre in Leicester and came second in the satisfaction survey, and Pure Planet, which came fifth in the survey.
Of the 72 Outfox the Market customers surveyed last September, it came away with an overall customer score of 82 per cent. Octopus Energy got 80 per cent and Avro Energy, in third place, got 76 per cent.
Npower came 25th on the list with a customer satisfaction rating of 54 per cent. Scottish Energy was 34th with 55 per cent.
Which? said: 鈥淥utfox the Market is a newcomer to the energy market and was rated in our survey for only the second time this year.
鈥淔eedback reveals that customers are happy with all areas of its offering.
鈥淭he company seems to have significantly improved its customer service since last year, as customers are much happier with it than previously.
鈥淐ustomers clearly feel it lives up to its promise of saving them money as it gained a five-star value-for-money rating 鈥 the only company to do so this year.
鈥淚n fact, 96 per cent of its customers in our survey said Outfox the Market was either 鈥済ood鈥 or 鈥渆xcellent鈥 value-for-money. The average across all suppliers is 70 per cent.
鈥淭his is likely thanks to Outfox the Market鈥檚 tariffs often being among the cheapest listed on price comparison websites.
鈥淚t frequently launches new tariffs, and withdraws others, although one fixed deal currently available comes with exit fees of 拢30 per fuel.
鈥淥utfox the Market鈥檚 customers also rated the accuracy of its bills and how easy they are to understand as excellent and good respectively.
鈥淐ustomers gave Outfox the Market four stars for customer service 鈥 the highest rating for this measure achieved in our survey this year, which is shared by four other companies.
鈥淲e didn鈥檛 get enough responses to rate how Outfox the Market handles complaints, but according to data from Ofgem it only resolved 25 per cent of complaints within two working days in the first half of 2020 鈥 one of the worst records for this among the companies in our survey 鈥 and a below average 82 per cent within eight weeks.
鈥淗owever, it received the lowest number of complaints per 1,000 customers, of just over two.鈥
Outfox the Market said it now has more than 100,000 customers with plans to grow that to more than 250,000 in the next five years.
It says for every unit of electricity the firm takes from the grid, it replaces this with a unit generated from a renewable source.
Co-founder Keith Bastian said: 鈥淎t a time of pandemic, where people are spending more and more time at home resulting in higher energy bills, we at Outfox the Market clearly understand the situation everybody is in.
鈥淲e are proud and grateful to our customers who have recognised we have made a difference.
鈥淭his proves our direction of travel is the right one, but we also recognise we have a lot more to do to become a supplier of choice for all.鈥
