The 51-year-old Spaniard is well placed to comment on both multiple former World Champions because he worked closely with them as a test driver when they raced for McLaren in 2007.
In particular, De la Rosa recalls a test in Bahrain where he was able to study the telemetry and compare his own performance with that of the duo who both missed out on the 2007 World Championship by a solitary point to Ferrari's Kimi Raikkonen.
But rather than the hot conditions that are generally found in Sakhir, the veteran of 104 grand prix starts believes it is on an evolving circuit when Hamilton and Alonso produce the ability that makes them so "special".
"I still say they are special. From the guys I worked with, definitely very special," De la Rosa, who will be working alongside Alonso next year as an Aston Martin team ambassador, told media including PlanetF1.
"Not every new driver that comes into Formula 1 is special. It's difficult to detect because all the drivers that come into Formula 1 have probably been special at one point in Formula 2, Formula 3, whatever. But then the reality comes when you're with these monsters (Hamilton and Alonso)."
Asked what it is about the duo that makes the difference, the 2006 Hungarian Grand Prix runner-up replied: "Adaptability…track conditions change.
"It's the fact every time you put on a new, or used, set of tyres, a good driver will need one lap and you think 'okay, the next one I can brake here or there'…it's too late, the track has changed, tyres have degraded, you have less fuel in the car, whatever.
"The good driver just has this sense that the grip is there. It's difficult to explain, but they know where the grip is without making too many mistakes because you can go over the limit.
"And then it starts raining, or you have front graining, or for example when the track is drying it's incredible how these drivers know where the grip is and actually make the gap bigger to the rest of the field.
"But the problem is the next lap, or the next 10 seconds, the track is a bit different, so it's difficult to judge from the outside because the track evolves more than the quality difference between them."