I've been using grid infill. I'm sure, pretty much any infill will work fine, but some infill types will require more infill than others for equivalent strength/stiffness. I used Gyroid infill for a while. It worked great, but I wanted the print to be faster, so started using grid instead.
As far as PETG goes, I've used Overture, Hatchbox and Polymaker brands without any issues. I did have trouble with PETG on my MK3S printer in the beginning. Admittedly, I didn't know what I was doing at the time. I've since got all that worked out as I learned more.
PLA is OK for bulkheads as long as you aren't in a very hot climate. I'm in Michigan and PLA is ok as long as it isn't exposed to the sun directly and/or the part is thick enough. Since bulkheads are inside (mostly) and thick, it isn't an issue. That said, I use PETG mainly because I, by far, have it most commonly loaded.