I have no knowledge of stainless types but have a couple of jobs to do so need to order a few stainless tig rods. Which would cover most tasks it seems a bit of a mine field to a new user?
I've always used 316L rods for 304 and 316, as well as anything else stainless that isn't critical. Same at work, that's all we've ever ordered for both 304 and 316 chemical pipework.
With stainless general purpose, over-alloying isn't really an issue.
I think it would be 308/309 would be a little cheaper and also the "right" filler for more grades? But personally, I wouldn't bother.