Thanks for the opinions on "sankyuu", everyone. After reading all of them, I'm leaning toward using "danke" in the future as I use it in conversation myself sometimes. Though there's also something of a possibility that I'll use "sankyuu" in its romanized form.
@ghostdivision Not at all! Or not intentionally anyway. I can't deny that I might be avoiding finishing Saeki-san on some subconscious level, at least based on how I am as a consumer. However, consciously, this series was just so fluffily enjoyable that after I read it, I was immediately compelled to introduce it to a wider audience. And I wanted to get it to a good point relatively quickly, as it's kind of sad just finding a single chapter of a series. As far as Saeki-san goes, I'll likely be finishing the main story within a week from when I'm writing this post, by the way.
Edit: removed useless period.