Which episode did you prefer? TPOT 19 or TPOT 20?
Both are quite good, even if not perfect, and I actually don't think either is top ten worthy (even if I still enjoyed them). But I'll have to go with TPOT19, because even if I think TPOT20 was well written and I'm satisfied by One's backstory, I just didn't feel as emotional when watching it as I did with TPOT19.
It might be because I just personally like objects more than algebraliens. There are a couple of algebraliens (Two and Three) that I absolutely adore, but for the most part, my mind still interprets them as external forces who don't completely fit in with the objects (which might also be why I like season one and especially BFDIA so much, no algebraliens there).
I cried when watching TPOT19, even if I had already gotten spoiled a lot of it beforehand. I still tear up when watching it today! With TPOT20, I appreciate the story, but I'm much more emotionally detached. The only part that made me tear up even a little was actually Needle's dialogue with One.
Also TPOT19 has more Grassy in it so it wins :P