My favorite lower-tier villagers are Mitzi, Rizzo, Blaire, Katt, Melba, and Sparro.
Mitzi is by far my favorite villager, and I was a bit surprised to see that she was only Tier 3. She has been my favorite ever since I first started playing Animal Crossing, with ACGC. She was the first villager I met in the series, and she quickly became a favorite. When I got Wild World a week later, she was the first to move into my town, and later became the first to give me her picture. She is always nice, and often sends me letters with gifts attached. Plus, she's really cute as well!
Rizzo and Blaire were in my first City Folk town, and I really liked them, but I lost them when I stupidly decided to reset that town. I regret resetting that town so much, since the villagers and layout were amazing, yet for some reason I thought it could be better. Ever since I reset, I haven't been able to keep a town for more than a few weeks, and I quickly lost interest. I got Rizzo and Blaire into my New Leaf town thanks to a couple users on ACC.
Melba and Katt were in my cycling towns for a short time, but they really grew on me. Unfortunately, I had no way of transferring them to my main town, so I had to give Melba away on the cycling thread. Katt moved out of my town when I messed up my TTing while TTing for weeds, which sucked, because at the time, I temporarily had access to a second 3DS that I could've used to send her to my main town.
I saw a thread about villager birthdays on ACC, and looked to see if any villagers shared my birthday. I found out that I shared a birthday with Sparro, so I decided to look for him on the trading board there. I was able to get him for free, but only had space in my second town, so I had him move in there. I really enjoyed having him there, and he quickly became yet another favorite of mine. However, because of careless TTing, he ended up moving out of my town.