Who would win Fat Gogeta or Janemba?

Gogeta


"I'm neither Son Goku nor Vegeta. I'm the one who will destroy you."
-Quote by Gogeta from Movie 12-

Surname:Gogeta
Fusion [fusion dance] from: Son Goku & Vegeta
Born:in the fight against Janemba [Movie: The Film, Part 1: The Fusion]
Age:unknown
Gender:male
Race:Saiyan
Origin:Planet Vegeta
Hair color: blonde [as Super Saiyan Level 2]
red [as Super Saiyan Level 4 (GT)]
Eye color:turquoise [as Super Saiyan Level 2]
blue [as Super Saiyan Level 4 (GT)]
Family:
see Son Goku and Vegeta
Combat trainer:none
Combat strength:unknown
see also || Combat forces ||
Was killed by:nobody
Appears in:
Movie: The Film, Part 1: The Fusion [SSJ 2]
Fighting Techniques:all that Son Goku and Vegeta can do
Specialty:Can only exist for 30 minutes. As a Super Saiyan Level 4 in GT even only 20 minutes.


DBZ-Movie: "The Movie - Part 1 - Fusion"
Gogeta is the fusion of Son Goku and Vegeta when these fighters do the fusion dance. He doesn't appear in the TV series at all. He appears shortly at the end in Movie 12, after the fusion dance between Vegeta and Son Goku. It doesn't work the first time, however, because Vegeta thinks the fusion dance is monkey (Original Vegeta tone: "Am I a prima ballerina?") And does not perform the last figure correctly. This creates Fat Gogeta, whose appearance brings Master Kaio to despair and makes the fans cry tears of laughter. Only after Paikuhan interferes in the fight against Janemba does the real fusion dance succeed and Gogeta makes short work of Janemba.

Dragon Ball GT
In the final fight against Li Shenlong, Goku and Vegeta use the Fusion technique again, but in Super Saiyan Level 4, which creates the really "perfect" fighter.
(GT source)