You are welcome. Personally I use 30lb, but it will all depend on where you're fishing. Rocky areas will need at least 30lb.
Recently in a spinning article, the author also mentioned, that he actually cast further with the 30lb, than with his 20lb. Have to look it up again, but that basically made the choice for me.
I would also suggest having a spare spool on hand. Maybe 20lb on the one and 30lb on the other.
Also, when buying casting braid, you will also find that the Suffix brand has one with different colors, which you can use to quickly determine the actual distance, with each cast.