You can only use one fishing line type all your life...

[FishTank]

Fluorocarbon.  I have fished tons of different lines over the years and Fluorocarbon has worked the best for me so far. 

[Log Catcher]

For me it would be mono.

[new2BC4bass]

Mono or co-polymer.  Don't think I'd care which one.

[Wildbillb]

Yozuri hybrid or original stren

[DitchPanda]

Is it August or February? This thread is 4 to 6 months early! If I had to choose one is go copolymer...izorline xxx. I have 1 rod with braid and basically everything else is copoly. I do have a few with mono but could easily switch over.

[Maxximus Redneckus]

Big game 8lb mono...its good enough for me never a issue ...8 will fit a penn 713z or 3000 size spinning reel and a 4600 size abu ...the reels i use most 90% of the time ...i may move up to 12 if it gets rocky or woody

[The Maestro]

I'm already only using one type of line - braid. For everyone saying flouro. What about topwater baits?

[Dminor9]

A good friend of mine who was a fishing guide for many years, got me started on braid over tens years ago. Since then, I use braid exclusively. So Braid.

[.ghoti.]

If a friend told me I would only be able to use one if anything for the rest of my life, I would trade the friend in on a used dog, and shoot the dog. 

[Tatsu Dave]

14 hours ago, Fishingmickey said:

Ahyup, Fluorocarbon it is. Pass the  pl

FM

Nothing more I can add....already only use flourocarbon

[ike8120]

Copolymer

[Str8BraidPowa]

It's gonna be Suffix 832 for me. I prefer the power of the braid, a heavier rod, and the hook being my limiting factor. Then again I am kinda a meat head.

[Hulkster]

Sufix Siege mono. 

[NYWayfarer]

Mono.

[jtharris3]

Mono - Trilene XT to be exact.