I just got my own Platinum version last week and so far I've gotten 4 badges. I had just gotten fly and taught it to my Staravia, which is close to evolving into a Staraptor.
In Platinum I like to have a Tropius. If it has fly, defog, cut, and strength you only need a Bibarel for the other 4 HMs, freeing up space for other pokemon.
In HeartGold, I use Dragonite or Ho-oh, and in Soulsilver I use Skarmory. Platinum sees use of random ones. I don't remember Diamond, and I use random ones in the Hoenn games.
In Pearl I used my Staraptor Star for flying. In Platinum I used my Crobat Marx. In Soul Silver I used my Fearow Albatoss. White will be my first game since Emerald where I don't have a flyer as part of my main team. (Hoenn isn't much of a pain to walk through, barring the rocks north of Mauville)