Going back to basics, there are four developing agents that are potentially interesting in this context:
- metol (M)
- phenidone (P)
- hydroquinone (Q)
- sodium ascorbate or ascorbic acid (C)
Note that there are variant names (Elon for metol, for instance) and chemical variants (such as Dimezone S for phenidone) for many of these. Sometimes mix-it-yourself formulas need to be adjusted for some changes.
Many common developers, for both film and paper, are metol/hydroquinone (MQ) formulations. Metol is said to be "superadditive" with hydroquinone, meaning that the two work together more powerfully than either one works alone. Other superadditive combinations include PQ, MC, and PC. PQ combinations are somewhat popular. A few PC developers exist -- most notably among commercial products, XTOL, Agfa Neutol Plus (but
not others in the Agfa Neutol line) and Silvergrain Tektol. XTOL is intended for film, but Neutol Plus and Tektol are paper developers. I don't know of any commercial MC developers, although I have seen (and use one) MC mix-it-yourself formula (
Dead Link Removed). It's common to see two, and sometimes three, developing agents in a developer both because of superadditivity and because using two agents enables the developer to acquire the best characteristics of each agent.
Generally speaking, metol has minor health risks because people sometimes develop a sensitivity to the chemical, resulting in rashes when they come in contact with it. Various sources indicate that hydroquinone is the most damaging of these four chemicals to the environment, and may be a little more toxic to humans than the others. Phenidone and its variants seem relatively benign by comparison, at least in the quantities used. (Developers typically contain only about 1/10 as much phenidone as they would metol.) Ascorbic acid is also known as vitamin C, so it's not really a health threat. Thus, from a health and environmental safety perspective, PC developers are best. This isn't to say that MQ developers are on the level of, say, equal masses of plutonium or anything; but if you want to minimize risks, it makes sense to use a PC developer, or at least a PQ developer, rather than an MQ developer.
I'm unfamiliar with the Rollei developer to which you refer, gonzo74, so I can't comment on its composition. My own print developer of choice is
DS-14, which is the mix-it-yourself predecessor to the commercial Silvergrain Tektol. These are both PC developers and they work just fine for me. They produce results that are indistinguishable from those of Kodak Dektol, at least with the variable contrast resin-coated papers I generally use. (Some papers respond more strongly to changes in developers than others, though, so there might be differences in other developers.)
One other comment: The four developing agents I just described aren't the only ones; para-aminophenol, catechol, glycin, and others can all do the trick, and may be preferable for one purpose or another, either alone or in combination with other developing agents.
