I would say they’re all viable in any circle. HOWEVER, each of them, I would say, have their peak circles. But again, it’ll depend on your party set up. You don’t really need Chrono 3 if you don’t have a partymate that has long cooldowns. You don’t really need Linker at all if all your partymates are AOE based. Thaum is probably the most well rounded support and will be useful no matter what party set up you have. Thaum also has Swell Body which gives 2x exp and drop rate. But the other two are better at supporting specific party set ups.
All in all, I’d say Linker 1 is enough but C2 is best. Thaum 1 is enough unless your party’s DPS revolves around Magic damage, then go C3. Chrono 2 is enough unless, again, you have high CD party members, then C3 it is.
Like I said before, party make-up is your most important factor in deciding what you should go with.