You're asking a completely open ended question. Many variables go into what fork weight oil you use - Bike? Stock forks or aftermarket cartridges in them? What spring rates? How much do you weigh? What's your pace? What's your riding style (Are you a hard, late braker?) Brand doesn't matter as much as how old it is. I'd rather use new Wal-Mart Supertech fork oil (They don't make it, just using it as an example) than official Ohlins fork oil that has 3 seasons of riding on it.
Suspension work is a lot of black magic, and many changes to one piece affect other adjustments. My suggestion would be to find a local, reputable suspension guy, and work with him and let him make the calls for you. Chances are, he's got a lot more experience than you do with what works and what doesn't, and the easier you make his job (By going with whatever he recommends), the quicker and easier he can get the bike to work for you.