I chose v5. I love how it's so easy to look after them.
I dislike the fact that on the v3 and v4, you need to complete a game fully or your Tamagotchi won't lose 3g of weight. I hated the jobs and schooling of the v4, I could never be bothered to send my Tamagotchi to school nor play the extremely long games. Once I actually bothered to time how long it took to play the games. It took 1min 50sec to play Jumping Rope, THREE MINUTES to play Mimic, 1min 30sec to play Shape, TWO AND A HALF MINUTES to play Dance and 1min 40sec to play Flag. However I did manage to get the patience to raise all of the secret characters, including Makiko even though Dance takes forever to play. Oh and I also raised Oyajitchi as well.
I hate the antennas of all of the versions, including v5. I'm right-handed but I prefer using my left hand to work the buttons of a Tamagotchi. Now if I use my left hand the antenna just gets in the way.
Sorry for all of my ramblings.