I cannot see how anyone can bake up a nice sheet cake in a jelly roll pan
Using a 2" deep pan makes it easy. No torting; no filling - that's what a sheet cake is - just a rectangle cake w/o filling
Fill the pan w/batter at least 1/2 full - better if it's 2/3rds full. You will soon learn that a 12x8x2 pan uses one cake mix; a 12x16x2 needs 2 mixes.
Baking at 325 is right but I don't find any need for a flower nail in the center........won't hurt but isn't necessary
As for brand......I prefer Magic Line pans; have heard many say Fat Daddio is good too. And for size......match the size of the pan to the board and box sold as a '1/2 sheet' which means a 12x16x2 pan. For a 1/4 sheet pan size should be 12x8.
Get *OUT of the habit* of calling them '1/4' or '1/2' sheet cakes!
When someone asks for a say '1/2 sheet' ask how many they need to serve. The general public has no idea about sizes
I've had people ask for a 'full sheet' when they wanted to serve only 12-15 people!