They're set in completely different galaxies with completely different characters. Most fans do crossover, but not all; there's a significant faction of SG1 that turns their noses up at SGA (claiming it was the downfall of Stargate), and a significant faction of SGA that's *only* SGA. But then there are a lot of people who do both, and some people (like me) who are fans of SG1 but only casual fans of SGA (even though I did write a couple of SGA fics). Basically, it depends on who it is who's signing up. Most people would be okay with getting either, but not all? On the other hand, the biggest group of SGA only people were the John/Rodney slashers who we don't have to worry about (yay!). Maybe ask right before signups what people want?