Yes...and no. I only had Diamond, then later Platinum too and I picked Piplup both times (and more than the others on subsequent playthroughs too). This time, buying 2nd hand I started with Shining Pearl which I picked... you guessed it, Piplup! But when I got Brilliant Diamond I went for Turtwig. Decided to have a male character in BD with a Dark / Sandstorm team (Torterra / Honchkrow / Skuntank / East Sea Gastrodon / HIppowdon / Garchomp) and a female character in SP with a partial Hail team (Empoleon / Staraptor / Mismagius / Abomasnow / Weavile / Toxicroak).
Realise despite so many saves, I've only used 2 of those non-starter pokémon (Honchkrow and Staraptor). That's what is so great about pokémon, aside from needing to tough out the early routes without captures eventually (Turtwig has a Shinx to keep him company until we get Murkrow and Stunky), there are over 200 different team options in the DP dex alone!