There is a long list of different jetpacks in jetpack joyride. I see some of them are necessary for achievements, and they look cosmetically different, but I'm curious if they have different game physics (faster/slower lift, faster/slower descent). I haven't noticed a difference in the few I've purchased, but I haven't reached the higher end ones yet. As I've played the game a while, I've noticed that some obstacles are nearly impossible to avoid, and I'm wondering if that is made worse by the jetpack I'm using, or is just the nature of the game.
All of the Jetpacks handle exactly the same way. However, some of the jetpacks have a flame or other output that can harm scientists on the ground, and some of them are perfectly harmless, which is something to keep in mind for some of the 'don't harm any scientists' missions.
Sometimes you get unlucky with the obstacles, and once the game gets going really fast, a lot of it comes down to luck.
You can purchase the High Mobility gadgets (the Super Sneakers & Gravity Belt) if you what to change the game play physics.