I oppose both but reactionary is a meaningless term, it doesn't describe an ideology or belief it is just prejorative used when people want to sound too smart to say "dummy"
Something that is reactionary is archaic or outdated. A reactionary is someone who wants to return to the past in some form or function, to turn back progress. TERFs pretty unambiguously are reactionary, specifically on the issue of trans rights. Tankies spew authoritarian apologia more at home in the mouths of mid-19th century nationalists than in modern democracies.
Reactionary is used to attack people like a belief system, but it is not. It is acted like an ideology when it is just an insult, that's not to say I can't think the insult fits. But you can pretty clearly tell when something is an insult based on if anyone would reasonably describe themself as it. Just own up to it and insult someone if you want to rather than use tankie pseudoscientific slanders that justified killing and imprisoning "counter-revolutionaries".
The tankie belief system is that someone either ally or reactionary- don't accept their rules.