As the title says- is there a particular creature that you've tamed without any particularly great expectations, which they've promptly readjusted much higher than you thought they deserved?
My recent Ark discovery has been the humble Kentrosaurus. Given they're unmountable herbivores without saddle armour, I was previously ignoring them in favour of hyenas... who promptly got stuck under the map so often I installed a mod to be able to recover tames from under the map. I saw a few kentros with babies when I needed it for a 'claim a few babies', and thought, 'eh, they don't need saddles so why not?'
I have promptly discovered that kentros are very resistant to getting stuck under the map (though have the same issues as ankies with slowly edging down falls instead of dropping), travel with good speed, have great destructive potential, are easy to find, can be trapped or distracted with a basic thatch trap, and take minimal investment other than appreciating a long starve time followed by lots of berries/veggies while being tamed.
Also, and more importantly, they have the same weight stat as stegos and mammoths, which is completely insane given you're intended to be bringing five or so of the things out on a trip. Taking them out alongside your current harvesting dino means you can basically get an arbitrary amount of resources, which coincidentally mitigates their weakness of not having meat-healing by giving them some rest time while you gather up.
Kentros are thus one of the best escort dinos in the game, unless you count being carried around by a flyer as an escort. (Which is reasonable, but an argie needs a much higher level than a metal pick.)
Which dinos have you had similar pleasant surprises with? Please attempt to convert us to your unexpectedly good niche tames.