Grand Companies

[Sida]

Another thing that can factor in is that you do all sorts of GC turn ins in the main city of them and debending of playstyle you might visit them often or very scarcely and it easily becomes a hometown of sort. At least for me this factored in a bit since I like the gridania atmosphere rather a lot compared to its siblings.

[ChameleonMS]

The gear difference between the GC is moot at best. The real only difference between one GC and the next is how many players are in the GC. From whatever the reason, Flames is the largest, and generally the most dominant in PvP.
I have levelled all 3 to maximum rank; and settled on Maelstrom, because, as Sida said. Your GC town becomes your de facto home town. I like the expediency of layout of Limsa.