Hmm. I am indecisive also. I haven't been as indecisive for the longest time. I get what you mean by wanting to choose the BEST choice. You don't like making mistakes and you don't want to regret it.
My advice is to take it day by day. Don't fret too much about the choices that you make. You are putting so much pressure upon yourself and the things that have yet to be selected.
One thing that helps me is this mental coin flip.
Let's say for example; I'm not sure if I want to get Passion Tea at Starbucks or the Peach Green tea. I want both very bad. What I do is I assign each tea to a side if a coin. Then I flip the coin in my head and it lands on one side. I either go forth with it or I realize I actually want the specific tea more than the other. I get my tea and move on with my day. I am happy with the choice I made.

I hope that helped! I do this so quickly now that it's easy to choose something. I know "Next time, I can get the one I didn't choose to get."

Also when I am conflicted, I ask a friend. Or a parent. And really get serious about it and talk about it thoroughly.

Good luck