have to purchase a new liner and need help!

You would think I was buying a new car or something. I am having the most difficult time trying to decide.

My liner has lasted 15 years. I understand they are not made as well as back then. Mine was a 20 something, not sure mil or gauge.

Do I replace it with a 20 or 25 (most say gauge)?

Is lavari better than GLI or Swimline? Any one better than the other? warranty is different depending on which site you find but most are now 15 except for the Lavari. And yes, I understand they are really only guaranteed for 1 year and only on the seams. I just figure better warranty=better quality.

I am having a hard time not buying online because the prices are so much better than around here. Of course the locals say that buying online means the liner has sat in the heat/cold and is probably weak and brittle because of that. Can someone recommend (or are you allowed to recommend on here) a reputable online store? Cost is a factor.

I really need help. I am wasting way too much time online trying to decide.