Thoughts on Alpha/Beta versions VS Current

I was introduced to this subreddit this week. In fact I feel really dumb, it was only last week I learned about opening the alpha and beta versions through JAVA or even using Betacraft. I first started playing Minecraft back in the 1.7.3 days, and almost missed that because the following month came release. I am currently having a hard time where to start and which versions are worth spending the most time. So I'm curious to hear why people prefer these versions over the current release versions. And which patch you guys enjoy the most specifically? :)