I feed a mix of timothy hay (compressed bale from Tractor Supply) and Orchard Grass hay (square bale from a local hay seller). The orchard grass seems to have a lot more of a 'fibrous' aspect to it, but I just mix the two and the bunnies eat what they want.
Mold scares me to death, always has. I used to have horses and I've been paranoid about hay mold most of my life. I've seen it before in horse hay, it was pretty obvious, so I know what it looks/smells like. I get nervous about the hay I have now though, because I know rabbits are so much more sensitive to it than other critters (and horses are pretty sensitive to it). I've noticed a very slight musty smell on occasion, but haven't seen any traces of mold as of yet. I guess all we can do is remain vigilant. Heck, even feeding straight pellets won't protect you from possible mold contamination. It's everywhere!!!!! :x