Tough call, almost every new build is my favorite but...
Like the topic says, most newly finished projects become one of my favorites for a time but some still are long after the fact, with some I really don't know why...
I think knowledge of the effort and its perceived improvement vs actually awesomeness plays a big factor.
Case in point: my Hasegawa 1/450 USS Missouri
There are a ton of faaaar better Missouri's out there but mine is dear to me because it represents a challenge meet. The outcome being better than I expected. For years this project sat near completion with just hull rails, rigging and final paint job & weathering to do but I didn't care for the looks of her and kept putting it off. I finally decided to re-do parts that I felt I failed on and then finish her. I'm glad I did. Missouri is now one of my few models I feel is truly DONE.