If I could change one thing about the Playstation Vita it would definitely be the game slot. In order to insert a game cartridge, you must open the slot that is placed on the top of the Vita. When I first got my Vita, I had the hardest time the game slot. My nails aren't that long so I had to pick at it in order to open it. When I finally was able to open it, I noticed that my method of picking at the slot resulted in parts of the game slot being chipped. That's not cute for a device that I just paid almost $300 dollars for. If Sony had designed the game slot to be open like the 3DS I wouldn't have cosmetic damage on the first day with my Vita.
I could have avoided this problem by buying games digitally from the PS Store. It's actually better to buy games digitally as they are usually cheaper than owning the cartridge. The problem with that was having to buy a memory card big enough to hold all of the games I want to play. $99 for a 32GB memory card is simply too expensive for this gamer on a budget (especially after dropping $250 on the Vita.) I went with the 4GB which could maybe hold 2 Vita games on a good day.
Another thing I would change about the Vita is the location of the headphone jack. The headphone jack is located at the bottom of the PS Vita which has proven to be a pain. Having the headphone jack at the bottom of the Vita makes it hard to place the Vita onto my desk in order to watch the screen. This makes it annoying to watch movies on the Vita, especially when the sound from the built in speakers isn't that good. It would've been better to place the headphone jack on the side or the top of the Vita so I can plug my headphones in and be able to place the Vita on my desk for viewing enjoyment. I shouldn't have to hold the Vita in my hands at all times. If Sony considers redesigning the PS Vita they should really put my suggestions into consideration.