The Partagas Corona when properly aged is an extremely complex and flavorful cigar. Along with the Upmann and Ramon Allones the best Cuban corona on the market.
If you are looking for strong as in a LFD Chisel or some of the strong putrid Camachos then you will not find it in any Cuban cigar. For Cuban cigars with the most strength then here is a list of cigars that I feel are on the stronger side with some nice nose. Note that this list is for cigars that have been properly aged.
Partagas Seri Du Connoisseur 1
Upmann Monarchs and 2's
Monte 2
RyJ Cazadore
Bolivar CE
Partagas Lonsdale
Punch Super Selection 2
Quai D'Orsay Panatela
Punch Ninfas
Cohiba Corona Especiales
Fonseca Invicto
Yes young Cuban cigars in many cases will be stronger than properly aged ones. There are however many Cuban cigars that will get stronger the longer you age them. Upmann 2's and Monarchs are a couple of such cigars.
Strength for the sake of strength is a new phenomena that has happened in the last few years in the cigar industry. Mfgs are making strong cigars that have absolutely no balance because there is a market for them. For some reason there are a bunch of smokers who are looking for sheer power so they can get a buzz off the cigar. Cigars like these are not good cigars, they are just strong. When I smoke a cigar I am looking for complex flavors and enough strength to feel the cigars as I exhale the smoke through my nose. Cigars like the LFD Chisel and other cigars loaded with ligero are not cigars that I smoke or care to have in my collection. Yes I have tried a bunch of these cigars but none have made it into my rotation.
The strongest cigars I smoke are Opus X and Ashton VSG's, these are strong cigars but have plenty of flavor and complexity.