Rayman. By far.

Love the Prince of Persia series. The original was one of the first games I ever played (I still remember my dad tinkering with the soundcard until the music and sound effects suddenly sounded amazing). That's why I took an interest in the Ubi games in the first place. I bought the first trilogy from a discount bin as a 3-in-1 edition and loooved all three (even though two was a bit too teenage drama in my then teenaged opinion :P).

Special mention goes to the Anno games, wich I know is also not initially Ubis property (I started playing them with 1503), but they treated the series very well with 1404 arguably being the best game in the series and then traking it onwards to the future installemts. I'm looking forward to Anno 1800 as well.

Edit: And how could I forget Rayman?! I love Rayman! Rayman Legends is one of the best platformers ever made.

1. The Settlers
(created by German developer Blue Byte in 1993, developer and IP were bought by Ubisoft in 2001, a new Settlers game was just announced at Gamescom, will be developed by the creator of the first game, release is scheduled for 2019)

2. Anno
(created by - now defunct - Austrian developer Max Design in 1998, IP bought by Ubisoft in 2007, new game Anno 1800 is currently being developed in Germany by Blue Byte, release will be in February 2019)

3. Heroes of Might and Magic
(created by - now defunct - US developer New World Computing in 1995, IP bought by Ubisoft in 2003)

These are my three most favorite Ubisoft franchises,

Not Ubi franchises really, those were all existing IPs that Ubi bought - if we go by what Ubi owns, Might and Magic (not Heroes) would definitely be my pick, though they had no involvement in any of them except for lackluster X.

How, how in the heck is Rayman not on that list?

Hahaha

Your TOP 3 consists completely of games created outside of Ubi, funny.

And Heroes is now in Ubis hands? I did not know that. Did they ever release a game in the series after NWC crashed and burned? Hmm, I would love Ubisoft if they make a remaster of HoMM3. That would be awesome. This game in current graphics. I would lose hundreds of hours playing this game.

Outside of Assassin's Creed's historic set pieces, such as the modern world gameplay - the game is a mess.
The history behind Assassin's Creed is not exactly accurate. It is just like a Hollywood movie that is based on actual events, they take a lot of creative liberties.

HMM V, VI, VII - all Ubisoft published, though developed outside of Ubi.

At least they did something with Heroes - fuckers have been sitting on Might and Magic with no new game (bar very lackluster X Legacy, developed by same dev that did HMM VII) since they acquired IP.