[quote name='Dutchie' timestamp='1479768197' post='3179207']
Some strings have red or blue thread at the ends, what's the puropse of this?
Thanks
[/quote]
The main purpose of the thread (they're also known as 'silks' by the way) is either to identify the make/ model of string, or to convince you to change strings when they start looking frayed.
Other than that, the thread wrappings may have served a purpose a few decades ago, but I don't think they do anymore. My favourite brands of strings have no wrapping at all.
As to the best strings to replace the broken one with, my only advice is to change the whole set, all four strings , at the same time, otherwise the the new one will be noticeably brighter than the other 3.
What are the best strings?
That's a personal choice. I like DR hi beams on my Jazz, but other people will have other preferences.
The only way you will find our what you like best is by playing roundwounds/flatwounds/tapes of various brands and gauges, which, given the durability of bass strings, takes years.
Enjoy the journey.