I don't know where BuddyThePug is coming from about writing style. This is a conversation forum. Buddy needs to lighten up a little.
I agree with hamsamich. I have done both also. Ops will be MUCH more challenging than chemistry, but on the other hand, chemistry will be a little less stressful.
According to the plant, outages for chemistry can be slower than other departments, especially during the middle parts. Since you have an ELT background, RP support is always needed during the outage, so many plants will designate some chemistry techs to help RP.
There will probably be more overtime available in OPS, and like was said before more chance for advancement. But I have seen Chemistry Techs go to RO/SRO.
So either way will probably work out in the long run. What may influence your decision, at least initially, is where do you want to live and work? Who is hiring and what positions are they hiring? If you don't care where you live then the decision is easier. If you don't have a timetable then you can wait until the plant/area that you want is hiring, etc.