This got a little longer than I meant it to, but reading back through, I dont really see anything to cut out. Just skip to summary if you must :-p.
Depends. If any of the following are things you've ever thought about doing for profit, Chef's ring is absolute win: Tavnazian Tacos, Carbonara, Coeurl Subs, and Marinara Pizza by the slice (IF they ever put this in). If you're, say, a sushi/hedgehog/rabbit/cookies/pies/loljugs type of fellow, then go with the Cordon Bleu set.
On the off chance anyone reads this and doesnt actually already know this: the synth's mentioned for pro-ring are all synths with intermediary synths required, for which the HQ may not be used as an ingredient. Also, in the case of carbonara, your choices are level a cooking mule to 36, or get the ring. Trying to make money off of carbonara requires at least Tier 2 (and seems to take Tier 3 to certain asshats lately) which is either 87 or 107. That's 71 levels over the jerky synth. Personally, I went with levelling my wife's cooking to 36, but that's because I started doing carbonara when it came out, and the ring wasnt an option.
Personally, unless you have 100+6 (hocho and all gp items except signboard), I'd go with ring. Stuff like cookies and pies are very easy to make, and the 100+9 with support crowd kinda dominates there(either that or there's a massive amount of people buying gil, the numbers just dont add up otherwise). The stuff that requires intermediary synths is still pretty volatile, but seems to be easier for anyone who's NOT already at the top o the foodchain to make money off of. Hope this helped.
PS. Level fishing. No? Player search Wolfhero on Diabolos on ffxiah. K? Now go level fishing :-p