I'm not sure, but mine is the update that was out when I started playing Minecraft. 1.3-1.4, around that. :)
I have many different updates that happen to be my favorite. the first update i played was 1.2.5, Lots of nostalgia here. 1.4 was loads of fun in my opinion, I like to call it the Spooky Scary update cause it was released around halloween. 1.7 I really liked because the world generation was changed and there was new places to see and new items to use. 1.8 is my 2nd favorite update because of how much stuff was added to the game, such as banners, the sea guardians, Alex and much more. It made the game more diverse and fun to play. But my #1 most favorite update... is 1.9 1.9 is usually hated by most Minecraft players and i can see why, but if you really analyze whats in this update, i think its one of the best updates ive ever seen out of Mojang both Gameplay and Map-making wise. The combat was finally fixed where its a lot like other survival games where theres a cooldown on weapons like in Skyrim and other MMORPG games instead of the Jitter-clicking stuff like you see in DOTA and league of legends. All the updates i mentioned here were great, but 1.9 was the update i had the most fun with. with the new End generation and Dragon fight, the Elytras, the new enchantments and potions, all that great stuff. Its nice to know that these updates really show that Minecraft is far from dead. and that i do see a bright future for this game.
Alpha, etc. because it was the start of a brand new game, Minecraft. It's nice to have that feeling of "what will they add next?" on a new game.
Eh, I like Beta updates mainly because the game changed and is primarily focused on simplistic things. Back before everything was nerfed, and I played with my friends.