I found this on Tinycatridge.
In Tomodachi Collection:
- You oversee a community built entirely from Miis you elect to import – no one lives in your town unless you put them there.
- You do not directly control any on-screen character. Rather, you watch the Miis live and interact with each other, offering advice or help as needed. Even your Mii is an independent character.
- The town is pre-arranged. New locations unlock based on your progress re: the residents (how many there are, how many problems you solve, etc)
- You are constantly making money just by interacting with the Miis. Say a Mii tells you “I’m hungry.” You buy food, give it to the Mii. If he or she likes it, you get money. If he or she REALLY likes it, you might also get a gift. Gifts can be items meant to be used or treasures for collecting.
- The game doesn’t have the sheer breadth of stuff that Animal Crossing includes, but it has more potential characters to play with since you choose who lives in the town
- It’s strictly single-player. Streetpass/Spotpass does get you more items in stores, though.
As for the other stuff, There's more randomness in Tomodachi Life than in Animal Crossing. You can't make a mii friends with another if you feel like it. You either have to wait if one of them wants to be friends with them, or they have a mutual friend. Miis won't decide to leave the island if you don't play it for a period of time. You only really miss out on the daily island donations, birthday news, and whatever items spawn in the food, clothing, hats, and apartment shops if you skip a day.
The game does indeed have its own Mii Maker so you don't have to create a bunch of Miis on the one on the 3DS menu to send to Tomodachi Life. You could import Miis from the Mii Maker and also scan Miis from QR Codes. If you want to edit the ones from the Mii Maker or QR Codes though, make sure copying is enabled.
I had the game since June and I still play it daily. More so than Animal Crossing.