There are four common, and several more not-so-common, developing agents in B&W developers, especially print developers: metol (M), hydroquinone (Q), phenidone (P) and sodium ascorbate (C). (There are several variants on these, such as Dimezone S rather than phenidone or ascorbic acid rather than sodium ascorbate. These minor variants don't matter from health and environmental perspectives, AFAIK.) Many developers combine M or P with Q or C, as in an MQ developer, a PQ developer, or a PC developer. (MC developers exist, but are rare.) Less common developing agents include para-aminophenol, catechin, and various others.
From an environmental perspective, my limited understanding is that hydroquinone is arguably the worst of those I've mentioned, although I don't recall the details of why. (Possibly something about depleting oxygen in waterways?) The quantities you're likely to dispose of in a small home darkroom are tiny, though. From a health perspective, my limited understanding is that metol is the worst because some people develop rashes after repeated or prolonged exposure. OTOH, I've also seen claims that this is due to contaminants that were common in the past but that are less common today. If you want to do the absolute best thing from an environmental and health perspective, that then leaves you with PC formulations. My understanding is that phenidone is pretty benign, and of course ascorbic acid is also known as vitamin C, which of course we all need to survive.
Few commercial PC developers exist. For film, Kodak XTOL is the most common of these. Fomadon Excel is supposedly an XTOL clone, and Patterson has or had a PC developer, too, but I don't recall the name and I don't know if it's still available. For paper, Silvergrain Tektol and Agfa Neutol Plus (but
not others in the Neutol line) are the only ones I know of, but I don't know if Neutol Plus is still being made.
There are several mix-it-yourself formulas. Nicholas has provided a link to some of Patrick Gainer's early efforts along these lines. His later
PC-TEA and PC-Glycol have become fairly popular film developers, and XTOL clones like Mytol (same link) are also fairly popular. You could also check out Ryuji Suzuki's
Dead Link Removed and
paper developers. FWIW, DS-14 is the predecessor to Silvergrain Tektol. I use DS-14 myself. I use it with the replenisher, topping up my working bottle after each session, and it lasts forever that way, so it's pretty economical.
I can't comment on how any of these compare to (Ilford?) Multigrade's odor, since I've never used it. As others have suggested, you might consider stop bath, fixer, or general darkroom ventillation if you're getting headaches.
Of course, there are other ingredients other than the developing agents in any developer. Any of these could theoretically be bad for health and/or the environment. They tend to get less attention than other ingredients, though.
