In 2019, Hamilton won his sixth world drivers' championship in what was the first year since 2002 that didn't feature Alonso on the grid.
Heidfeld, who has 185 race starts to his name along with 13 podiums, states that he believes Hamilton is the fastest driver he came up against in F1.
However, the most rounded driver accolade from the German goes to Alonso, who won two world titles with Renault in 2005 and 2006.
“I would say the most complete [driver] is Alonso,“ Heidfeld said on the Beyond the Grid podcast. “Probably the most talented is Hamilton but the best overall, in my eye, was Alonso.
[Alonso] is, for me, definitely the guy I would like to see most back in Formula 1. When he stopped, when he quit, I thought then I would like to see him race again because he is, for sure, one of the best.”
“He was world champion, but he would have deserved to be world champion more times.”
Heidfeld added that Alonso was the driver he enjoyed racing the most as he, for the most part, kept it fair.
“It was fantastic to watch him, and as extreme as he was sometimes out of the car, some stories you hear, what he did in the team and how he played certain things, which in the end probably were also not always to his own benefit.
“I did love to race against him. He was probably the driver I enjoyed most racing against on the circuit because he was always fair – well, not always! Most of the time!”
Bahrain International Circuit - Winter testing