More important than which line is how you store & use it.
If you are domestic user and buy a big spool keep it under water.
Trimmer line is cellulose based plastic so it biodegrades.
It is also heavily hydrated ( has a lot of included water ) and will dry out and go brittle if exposed to air and will do this a lot quicker at higher temperaures and in direct sunlight.
VU from the sunlight also attacks the plastic. so dark, cool & wet is best storage.
Next is how you use it.
Domestic users tend to run the line till it breaks off.
This causes the line inside the spool to fret and weld together which decrases its strength dramatically when you finly get the !*##!@* out of the trimmer head.
So if you are using a self feeding head, bump it very regularly ( about every 20 to 30 seconds ) and you will get the best out of whatever line you use.
You also will save a lot of time as you will always be cutting with the full length of line the head will spin and not be spending 1/2 your time pulling the head apart to retrieve the broken off end.
The smaller 1/2" to 1" bits than end up n the lawn will be less obvious particularly if you use a black line which because it is black will brake down faster.
I spend a lot of time teaching my customers how to use their trimmers properly and it is amazing that some who used to go through 1lb reels every season are now back to a 4 oz donut pack.
As for shape, the twisted line is quieter and IMHO lasts longer & cuts better.
In theory the star, triangle & square sections should cut cleaner but I hane tried them all and have not seen any significant difference,