You want to pick up and return 4 different times? Seems like quite a hassle. I would do a search through the threads and you can see what people have found. There is already a Sixt @ LAX Thread too.

Car brands are not guaranteed by the way, but they can try to hold your preference.

Car categories are very similar to those of National. Off the top of my head, I know these.
PCAR- A3, CLA
LCAR- 3 Series, ATS, A4,
XCAR-5 Series, XTS, A6
XFAR - GL 450, Escalade (I believe ML is in here too)
Don't know LFAR but I think its Caddy SRX?