For me wire has always been a question of money and how much I thought I could afford at a given time.
When I was a young man during the Depression (the Great One not the one we're in now) I built with an eye to conserving money since money was scarce so I used the cheapest wire I could find but even then I would only use 1" poultry wire.
I used one inch because in those days we used a lot of brood hens and let the broods range in the pens. 2' poultry wire would obviously not work in this instance as the brood would walk through the wire of its pen into other broods but without the hen causing all sorts of issues. Likewise, rats and predators were more deterred with 1" wire.
Today my grandson is embarking on a new venture into poultry and is building a new compound of coops and runs. He has involved me a good deal (mostly out of kindness since really he doesn't need any help) and I've gotten to know a fair bit about what is available in wire today.
Today's galvanized wire, much the same as then, comes in 14. 16, and 20 gauge either galvanized before bonding or dipped after welding. After welded galvanize is the best since the welds are galved making it last longer and more rust resistant.
There is also now galved after weld with a PVC vinyl coat for about $200 for 20g 6'x150' and this I think is a really good buy if you think how long it will last.
There is also hard-wire PVC Vinyl coated welded after galvanized in 1" x 1" or 1" x 2" which is excellent for chicken runs and very predator resistant. For the 14 gauge 1" x 2" 100" long I've seen it available in PA are for under $400 per roll.
Hard-wire is the way to go but with UPS or freight Shipping is quite a good deal of money.
Depending on your needs and amount of wire Lowes and Home Depot have several selections of PVC coated wires that would make good choices for pens.
What ever you chose, I always say spend the most you can afford on the wire now; since you will either replace it in 3 years or 30 depending on what wire you went with in the first place.
If a hobby that may not last go cheap. If a passion that will last you a lifetime like me go with the best you can afford!